Mayumi Ōuchi (大内麻由美, Ōuchi Mayumi, born 16 May 1979) is a Japanese professional darts player who plays in World Darts Federation (WDF) and other national events. She is a five-time Japan Open champion and she representing her country eight-time at the World Masters, where she four-time advanced to the quarter-finals. One of the most successful darts players from Japan and first WDF World Cup women medalist from this country.