PURPOSE: To provide the title agent effective for inhibiting nephropathy promotion, containing, as the main ingredient, Fructus crotons extract.

CONSTITUTION: The objective agent containing, as the main ingredient, Fructus crotons extract (obtained by removing Fructus crotons oil, one of the components of Fructus crotons, from Fructus crotons) which has been used as a cathartic or diuretic for a long time. For the administration of the present agent, peroral administration is especially preferable, its dose, in terms of active ingredient, being pref. 100mg-10g a day per adult in one to three portions a day.