List of ''Ben 10: Alien Force'' episodes

After setting aside the Omnitrix some years ago, 15-year-old Ben Tennyson discovers his Grandpa Max has disappeared. Inside Max's RV, Ben finds a Holo-viewer with a recording from Max and he asks his cousin Gwen for advice as they meet Magister Labrid, an agent of the Plumbers and Max's partner in a case he was working on. They go to a train station where an arms trade between the Forever Knights and the DNAliens, brokered by Kevin Levin. Ben tries to dial in his alien on his Omnitrix, but it reboots and recalibrates into a thin watch with a color scheme of green and black, giving him access to 10 new aliens. The DNAliens get away, the Forever Knights escape with one of the weapons crates, and Kevin is captured. The Plumber asks Kevin for help in finding the Knights' hideout.

The group runs into an army of Forever Knights. In the confrontation Magister Labrid is killed when he saves Kevin's life, and Kevin joins Ben and Gwen on their search for Max to repay his debt. Gwen is able to trace a leftover Laser Lance back to its original owners, and they soon find a secret underground base infested with DNAliens. Sneaking in, the find that Max isn't there anymore, and on their way out, they see that the Highbreed in charge of the ship.

The authorities of a local town named Grover's Mill arrest a half-human, half-Pyronite boy named Alan Albright for arson and criminal damage. He is wearing a Plumber's badge, which leads Ben, Kevin and Gwen to Alan, thinking Alan's badge is Max's. Elsewhere, Alan uses his pyrokinetic/thermokinetic abilities to escape the officers, and the resulting damage to a building leads the team to believe that Alan may have hurt Grandpa Max. Ben soon discovers that the DNAliens are responsible for the damage, having built a huge, needle-like weather machine in the corn fields.

Kevin meets with an old friend named Argit, who claims he knows the location of a particular piece of alien tech Kevin is looking for. Needing something to bargain with, Kevin steals Max's RV, the Rustbucket, but Argit double crosses Kevin and steals the RV for himself, after seeing the huge amount of Plumber's tech and weapons inside it. The team follows Argit with a tracking device that Kevin hid on the Rustbucket's undercarriage and stops Argit, but Kevin storms away to seek out Vulkanus, who is in possession of the alien device. Kevin tries to make a deal with Vulkanus, but the later forces Kevin absorb a rare alien crystal called Taedenite, planning to use him as a living gem mine.

Ben, Gwen, and Kevin set out on their mission to locate other Plumbers' children and they encounter Michael Morningstar. Since he has all the Plumber's gear of his late father, as well as the fact that he seems to have been helping his city using his energy-controlling abilities, Ben and Gwen are quick to trust him. Kevin, however, remains suspicious. Finding a group of zombified school girls at a power plant, the team engages in a short battle, and Michael "accidentally" lets them escape. Kevin later discovers Michael is making the zombies, draining the schoolgirls of their vital life-force energy and then commanding them to collect more strength for him. Gwen sees through Michael's facade and takes back her energy for herself. Kevin crushes Michael's Plumber badge after Ben's team defeats him, telling him he doesn't deserve it.

Gwen tells Ben to ask Julie to go on a date with him to a local boardwalk amusement park, the Pier. After Ben attempts to ask her out, Julie agrees. Elsewhere, out in the forest, a small dog-like Galvanic Mechamorph seeps out of a crashed spaceship. Seeking a Plumber's badge signature, the Mechamorph soon finds Ben and starts taking control of the rides to get Ben's attention. After a few failed attempts, the alien then uses a ride to kidnap Julie. In the process, Julie finds out about the Omnitrix. The two follow the Mechamorph to the crash site. The Galvanic Mechamorph, accidentally given the name Ship, is reunited with his owner, Baz-El, another Galvanic Mechamorph who looks more human. He leaves Ben and Julie in peace.

While Ben, Gwen, and Kevin are taking a break at Max's favorite fishing spot, they see a mysterious cloaked woman leave a flower at the base of Max's favorite tree. When the team tries to meet her, she disappears. They decide to stake out the area for a while until the woman shows up again. The woman shows up, and is able to beat both Ben and Kevin in battle with ease. However, when she sees Gwen use her powers, she is amazed. As it turns out, Gwen's magical powers are in fact inherited from the strange woman, who turns out to be Ben and Gwen's long-lost paternal grandmother, Verdona, who is an immensely powerful energy being called an Anodite from the planet Anodyne. She attempts to convince Gwen to break out of her human body and embrace her full Anodite power, but Gwen refuses, even after a long fight. Verdona leaves, but promises it won't be the last time she asks her.

After the team faces off against a Techadon robot, Kevin grabs the severed hand of the robot and places it in his trunk. At night, Ben's childhood bullies J.T. and Cash Murray see Kevin's car outside a restaurant, and decide to wreck it. They push it down a hill, smashing the trunk open. They look inside and grab the Techadon gauntlet before the car's alarm attracts Kevin. Back at their hangout, Cash puts the gauntlet on, planning on using its built-in laser blaster to destroy Ben once and for all and repair their reputation but the full robot armor begins to reform around Cash's body. In doing so, the arm messes with Cash's mind, making him more hostile than usual. Ben fights Cash, and J.T. attempts to reason with him. After remembering his friendship with J.T., Cash's willpower overrides the robot arm, and it gradually reduces in size to the point where Cash can take it off. J.T. and Cash walk away with a newfound respect for Ben.

The Incursean Emperor Milleous's daughter Attea is kidnapped by the bounty hunter Sevenseven. Unless she is returned, Milleous plans to destroy the Earth. The Emperor's majordomo, Raff, seeks out Kevin to help on the search. Using Gwen's powers to track her, they teleport to a nearby dam to rescue her. When the dam is broken , Ben uses the untested Alien X to try to fix it. The task proves simple thanks to Alien X's vastly strong reality-warping capabilities, but Attea is yet again captured by Sevenseven and Ben finds himself locked inside Alien X in endless debate with the alien's other two personalities, Bellicus and Serena, unable to move or transform back without their consent. Meanwhile, Kevin and Gwen struggle against the Incurean forces attacking them at all sides. Eventually, Ben is able to convince Serena to trasform him into Swampfire, and makes quick work of the enemies. The team completes the job successfully, and Milleous informs them that Earth will be spared.

Paradox and Azmuth arrive on Earth to warn Ben of the approaching Highbreed fleet. Gwen and Kevin gather all the allies they've met (Alan, Cooper, Julie and Ship, as well as their enemy Darkstar) to counter the threat. Meanwhile, Azmuth reveals to Ben that the Omnitrix contains the DNA of every sentient species in the galaxy, 1,000,910 in total, and unlocks the Master Control so Ben can effectively combat the Highbreed.

Ben begins by recapturing the lost aliens of Chromastone, Spidermonkey, and Goop before taking on Vilgax. However, despite trying to use Jetray, Big Chill, and Humongusaur he is unable to defeat Vilgax. Gwen and Keving show up with Way Big, who Ben scans and attempts to transform into, but he becomes Chromastone instead. Vilgax smashes Chromastone and Psyphon picks up the Omnitrix, but then Ben reappears as Diamondhead and defeats Vilgax, saving the Earth.

Ben and the team travel to an alien planet to resolve a conflict between the inhabitants. Kevin finds the Argit has been selling the weapons from one side to the other after painting them a different color. A temporary truce occurs, but as Ben attempts to shake hands with the leaders of each side, one side takes offense and the war restarts. Then Ben kidnaps the leaders of each side to attempt to force another truce, but they escape after blinding Ben with a flashlight. Ben transforms into Way Big and accidentally breaks a statue of the planet's former leader. With both sides fighting angry at Ben, he flees the planet.

Vilgax asks for Ben's help to take down Zs'Skayr who has taken over his planet.

The Omnitrix malfunctions, turning Ben into a ruthless and aggressive alien while on an intergalactic peace mission.

Vilgax and Albedo return and team up to kidnap Kevin and Gwen so that they can take down Ben.

Ben gives up the Omnitrix and overcomes seemingly impossible odds to defeat Vilgax, who has betrayed Albedo.

Elena, a childhood friend of both Ben and Gwen, as well as a Plumber's kid, returns to explain that her father has been abducted and that she needs their help.