The widely anticipated decision comes with No. 3 Kentucky approaching postseason play, and coach Rick Pitino has said that Mercer's announcement would remove a distraction from the team.
"Certainly Ron Mercer has been someone special for us the past two years," Pitino said. "He helped us win a championship last year. He's been a humble, hard-working player since the day I met him."
Mercer, a finalist for player of the year awards, is averaging 18.1 points and 5.3 rebounds a game and is expected to be one of the top selections in the June draft.
The 6-foot-7 sophomore from Nashville, Tenn., recently took out an insurance policy that would pay him $500,000 in case of a career-ending injury during the rest of the season.
Mercer's teammate, Derek Anderson, sustained a season-ending knee injury Jan. 18.
"The thing that happened to Derek made me think what could happen to me," Mercer said.
Mercer said he talked with his parents last week about turning pro. He said his mother wanted him to get his education.
"She told me to take some time out and think about it," Mercer said.