Provided are a novel renal failure progression inhibitor, prophylactic agent for renal failure, and indoxyl sulfate production inhibitor, intended for human use, in particular, for a patient with renal failure. The renal failure progression inhibitor, prophylactic agent for renal failure, and indoxyl sulfate production inhibitor each comprises paramylon derived from Euglena or a processed product thereof as an active ingredient. In the case of the renal failure progression inhibitor, for example, paramylon is continuously orally administered to a patient suffering from chronic renal failure, undergoing a dialysis therapy, several times per day in a dose of 1 to 5 g per intake. In particular, the renal failure progression inhibitor is singly administered to the patient in a capsule or powdered preparation at a prescribed time interval before and after administration of other drugs.