The announcement ended months of speculation that Enzi would join the cadre of GOP lawmakers who won't be seeking re-election.
The Hill reported that the doubts arose after Enzi was angered when Republican leaders declined to appoint him to the Senate Finance Committee.
According to the Hill, Enzi couldn't resist teasing a crowd of supporters in Gillette Saturday by delivering what sounded like a retirement speech. He ended it, however, by saying, "Now I'm asking the people of Wyoming to renew my contract."
Five Republicans have announced their intentions to leave office at the end of the 110th Senate. No Democrats are leaving.