Sen. Mike Stack of Philadelphia announced his change in plans Thursday.
Also Thursday, U.S. Rep. Bob Brady of Philadelphia, who had supported Stack for governor, endorsed U.S. Rep. Allyson Schwartz in the eight-way Democratic gubernatorial race.
Stack campaign spokesman Ken Snyder says Stack opted not to run for governor because it would be difficult to raise enough money to be competitive and because so many of the candidates share his views on the issues.
At least three other Democrats are running for lieutenant governor.
Candidates for governor and lieutenant governor run separately in the primary and the winners are joined on party tickets for the general election.