Kim beat Hungary’s Tamas Lorincz 1-0, 2-0 to give South Korea its first wrestling gold of the London Games.
Iranian world champion Saeid Morad Abdvali was knocked out in the quarterfinals by France’s Steeve Guenot. Kim beat Guenot, the Olympic champion in 2008, to reach the gold medal match.
Kim’s biggest win had been the Asian championships in 2010.
Georgian Manuchar Tskhadaia and Guenot won bronze medals.