Episode 01 :-  And Then There Were 10
In Episode 01, Ben Tennyson a 10 year old boy after the completion of school goes to spend his vacations with his Grandpa Max. To his Surprise Grandpa Max also invites her cousin sister Gwen Tennyson. They both woth Grandpa Max in their own Rust Bucket goes for a summer camp. There a meteror crashed Ben was outside the camp for walking. He sees the meteor and chases him. He sees a device containing a watch inside it which get attached on Ben's hand and give him the ability to transform into 10 various aliens who possess different power.

Episode 02 :-  Washington B.C.
In Episode 02, Ben 10 chases the theives who stole Jwellery shop and the thieves pit oit the fire in house so as to distract Ben. Ben saves the people of hoise until then the thieves were chases by Grandpa Max and Gwen with Rust Bucket. After then Dr. Animo appears after 5 years who was disappointed by not getting the prize for his experiments so he made a transmodulator and make his from in a giant frog Bullfrog and he also made a bird giant.

Episode 03 :-  The Krakken
In Episode 03, When Ben and Gwen go on a fishing trip they came to know about the giant creatue in the lake known as Krakken. Ben has to stop him. He came to know about the reason of upset of creature. The Krakken was upset because someone was stealing his eggs.

Episode 04 :-  Permanent Retirement
In Episode 04, Ben , Gwen and Max visit to their Aunt Home Aunt Vera where they saw that the shape shifting aliens known as Limax are kidnapping the inhabitants of that area and replacing them with their version. Grandpa Max is also changed and Ben amd Gwen resolve the problem as Water is the weakness of Limax.

Episode 05 :-  Hunted
In Episode 05, Vilgax wants that Omnitrix from the Ben so he hires Three hunters Kraab, SixSix and Tetrax to take back the Omnitrix to Vilgax. One by One Ben can handle them but all at a time was a big problem for Ben. Tetrax changes his side and fights with Ben.

Episode 06 :-  Tourist Trap
In Episode 06, In a Town Sparksville known for the tourism, Ben and Gwen had a fight and Ben afyer turning into Four Arms releases the small creatures elerctic aliens Megawhatts who are very mischievous. Ben turns up into Heatblast and he catch all of them in a fishing pod with a better plan.

Episode 07 :-  Kevin 11
In Episode 07, After being angry from Grandpa Max Ben wants to spend some time alone so he gets oit of Rust Bucket and then he meets Kevin 11, An osmosion. Ben reveals him that what is Omnitrix. Kevin plans to do evil by absorbing the energy from Omnitrix. This leads the fight between the two.

Episode 08 :-  The Alliance
In Episode 08, A villain named Rojo steals the money from Bank. Ben and Grandpa stop them but Max hets injured in this while. When Ben fights with Tojo again he seea that she is controlled by Vilgax Robots.

Episode 09 :-  Last Laugh
In Episode 09, Gwen and Max visits a Travellung circus. Ben was always afraid of Clown so he decides not to come. After the Circus is Over all the people's soul was stolen by the evil clown Zombozo who has more 3 evil submasters. Ben beats them with Wild Mutt but disappears when Zombozo arrives. Ben fight against Zombozo as Ghostfreak the scariest alien of Ben and releases the soul of every people.

Episode 10 :-  Lucky Girl
In Episode 10, Ben ha fight with evil magician Hex during which Ben got Hex's One of the magical charm (Lucky Charm) and gives it to the Gwen. After understanding the power of Chatm Gwen suits up and becomes 'Lucky Girl'.

Episode 11 :-  A Small Problem
In Episode 11, A small problen occurs in Omnitrix due to which Ben stuck in its alien form Gray Matter who is captures by Howell on pool. Later they both are captured by the Forever Knights who plans to control all over the world. Ben as Gray Matter finds their Weaponry and blast it and their whole Base.

Episode 12 :-  Side Effects
In Episode 12, Ben has a cold which has side effects on his alien forms and their power wad becoming useless but heat blast power with cold are used as a weapon against a insect type villain Clancy.

Episode 13 :-  Secrets  [ SAESON 01 FINALE]
In Episode 13, Vilgax want to take the Omnitrix at any cost. He personally warns the Ben in dream. This makes Max worries but Ben takes it normal. Vilgax was waiting for the use of Omnitrix to locate them. Ben uses Omnitrix and Vilgax held it on his spaceship. Max went to Mount Rushmore and get some help to release the Ben and tell Vilgax about Self destruct mode. Then they all of three flew leaving Vilgax on ship and it explodes.