Phelps entered his plea to a charge of driving under the influence in Baltimore City District Court on Friday morning. He was sentenced to a year in prison, but the prison sentence is suspended. He must be on probation for a year and a half.
The 18-time gold medallist was arrested on Sept. 30. Documents show that the 29-year-old Phelps was leaving the Horseshoe Casino in downtown Baltimore when he was pulled over for speeding and crossing the double yellow line while driving in a tunnel. Police say Phelps registered a .14 per cent on a blood-alcohol test. The legal limit to drive is .08 per cent in Maryland.
A week after his arrest, USA Swimming suspended Phelps for six months.
Phelps entered a six-week treatment program in October. This is his second DUI conviction. Phelps pleaded guilty to drunken driving in 2004 in another Maryland county.