Season Two ( Book 2 : Earth ) of Avatar : The Last Airbender , an American animated television series on Nickelodeon , first showed its 20 episodes from 17 March 2006 to 1 December 2006 . Season Two ( Book 2 : Earth ) of Avatar : The Last Airbender , an American animated television series on Nickelodeon , first aired its 20 episodes from March 17 , 2006 to December 1 , 2006 .