(R)-(+)-5-hydroxy-1-methylhydantoin is an optically active substance having an excellent suppressive action of the progression of renal failure. At an administration to a model animal of renal failure, (R)-(+)-5-hydroxy-1-methylhydantoin significantly suppresses an increase of creatinine in blood as compared with the S-form and the racemate, and shows an excellent suppressive action to the progression of renal failure by improving creatinine clearance. Thus, (R)-(+)-5-hydroxy-1-methylhydantoin is useful as a highly-active agent for renal failure.