An object of the present invention is to provide a pharmaceutical agent which is administered to a patient with chronic kidney disease in which the progress of worsening of renal function is rapid whereby the progress of the symptom is suppressed or improved.The present invention relates to a progress-suppressing or improving agent for chronic kidney disease containing 5-hydroxy-1-methylhydantoin as an active ingredient. The pharmaceutical agent of the present invention showed a significant effect in a patient with chronic kidney disease where progress of the renal function decrease is rapid. The present pharmaceutical agent is very useful as a highly safe pharmaceutical agent which suppresses or improves the progress of worsening of the renal function of a patient with rapidly progressive chronic kidney disease for which there has been no effective therapeutic agent being simply and easily ingestible.
