An object of the present invention is to provide a production method for an R—Fe—B based sintered magnet having a plating film excellent in adhesiveness on the surface thereof, by conducting a series of processes of acid cleaning and smut removal as pretreatments of an R—Fe—B based sintered magnet, and the subsequent plating treatment effectively without causing trouble. The production method of the present invention includes a series of processes of acid cleaning and smut removal of a magnet as pretreatments, and the subsequent plating treatment is conducted consistently with a state, in which the magnet is placed in a barrel made of synthetic resin. The smut removal is conducted by ultrasonic cleaning of the magnet with rotating the barrel in water in which the dissolved oxygen amount is set to 0.1 ppm to 6 ppm by degassing.