Various analogues of benzyl 5-phenyl-2-oxazolecarbamate (1a) were synthesized, and the structure-activity relationship of these analogues as aldose reductase inhibitor was studied. The carbamate group was necessary for the inhibitory activity. The introduction of an alkyl group at the C-4 position of 1a enhanced the inhibitory activity, however, the N-carboxymethyl group on the carbamate moiety counteracted to a hydrophobic interaction between the alkyl group at the C-4 position and the enzyme molecule.