Powdery scab is a skin disease of potato tubers caused by Spongospora subterranea. The effect of a special fertilization method on powdery scab in potato was investigated in the soil area of Eutric Fluvisols in the Oshima region of Hokkaido, Japan. In the growing stage of the potato tuber, the pH of the soil layer where the potato tuber grows was significantly lower when ammonium sulfate was supplied in the rows and phosphate and potassium were supplied throughout the surface soil (special fertilization) than in that of the control group, where all fertilizers were supplied in rows. In the flowering stage, the pH was 5.5 in the control group and 4.5 in the special fertilization group. The occurrence of powdery scab decreased in the special fertilization group. The scab index was 60 in the control group but 26 in the special fertilization group. The average aluminum concentration in the water extraction was 0.35 mg L^<-1> in soil at the pH 4.5. It is estimated that the aluminum concentration in the water extract must be more than 0.5 mg L^<-1> for suppression of the scab severity index to less than 10.