Frank spoke Monday at a news conference in his hometown of Newton.
Frank said he originally intended to run for one more term, but that his decision was partially due to the fact that the state's new redistricting map will include many people he has never represented before.
Frank said he has had a "busy and stressful" four years dealing with financial reform after the recession.
He says he plans to write and stay involved in public policy decisions.
The 71-year-old Frank, and a lifelong liberal, won a House seat in 1980 was one of the first lawmakers to announce that he is gay.