The present invention provides a method for treating diabetic vascular complications including administering to a subject in need thereof a therapeutically effective amount of an extract product of a Dioscorea species. The extract product preferably is prepared by a process which involves (a) extracting a tuber of the Dioscorea species with an alcohol-based solvent in the presence of an acetic acid solution to form an extract composition, (b) subjecting a resultant product obtained in step (a) to obtain a soluble fraction, and (c) removing solvent from the soluble fraction obtained in step (b) to obtain the extract product.