Disclosed is a rhodanine derivative of formula (I).A rhodanine derivative of formula (I) ##STR1## wherein R.sup.1 is hdyrogen, C.sub.1 -C.sub.8 alkyl, carboxyl(C.sub.1 -C.sub.4)alkyl or (C.sub.1 -C.sub.4)alkoxycarbonyl(C.sub.1 -C.sub.4)alkyl;R.sup.2 is --CH.sub.2 --CH.sub.2 --R.sup.3, CH.dbd.CH.sub.m R.sup.3 (m is 0 or 1), ##STR2## (R is C.sub.1 -C.sub.3 alkyl) or --CH.sub.2n CONHR.sup.4 (n is 0 or 1-4); R.sup.3 is a thienyl or furyl group which may be substituted by C.sub.1 -C.sub.3 alkyl or halogen; a pyrrolyl group which may be substituted by carboxy(C.sub.1 -C.sub.3)alkyl on the nitrogen atom; or a phenyl group which may be substituted by one or more substituents selected from the group consisting of C.sub.1 -C.sub.3 alkyl, C.sub.1 -C.sub.3 alkoxy, hydroxyl, halogen, trifluoromethyl, carboxyl, (C.sub.1 -C.sub.3)alkoxycarbonyl, cyano, carboxy(C.sub.1 -C.sub.3)alkoxy, (C.sub.1 -C.sub.6)alkoxycarbonyl(C.sub.1 -C.sub.3)alkoxy, benzyloxycarbonyl(C.sub.1 -C.sub.3)alkoxy, piperidinylcarbonyl(C.sub.1 -C.sub.3)alkoxy, 2H-tetrazolyl, 2H-tetrazolyl-(C.sub.1 -C.sub.4)alkoxy, carboxy(C.sub.2 -C.sub.4)alkenyl, (C.sub.1 -C.sub.3)alkoxycarbonyl(C.sub.2 -C.sub.4)alkenyl, carboxy(C.sub.1 -C.sub.3)alkyl and (C.sub.1 -C.sub.3)alkoxycarbonyl(C.sub.1 -C.sub.3)alkyl; andR.sup.4 is a phenyl group which may be substituted by one or more of the same substituents as defined above, or a pharmaceutically acceptable salt thereof.The derivatives are of an inhibitory activity against aldose reductase and useful for the prevention or treatment of complications of diabetes.