The present paper describes the serum cholesterol level lowering effect of the underground parts of Rosa rugosa(Rosaceae) which have been used in a folkloric medicine for treating diabetics. The methanol extract was shown to lower the serum lipid level against the normal and 1% cholesterol and 0.5% cholic acid diet feeding to rats, respectively. When various fractions prepared from the above methanol extract was administered, the ethyl acetate-soluble fractions lowered the serum cholesterol level most remarkably. And when (+)-catechin from the ethyl acetate-soluble fractions was only administered to them, the serum cholesterol level was significantly lowered to 260$pm$9.3mg/dl, the decrease of 17% for the control group. Therefore, it is suggested that (+)-catechin is one of the active principles of this plant.