Objective： To investigate the inhibitory effect of Epibueropyridinium A on aldose reductase. Methods： Aldose reductase was extracted from cattle crystalline lens. Besides Epibueropyridinium A, the reactive system also contained DL-glyceraldehyde, aldose reductase, and NADPH. The activity changes of aldose reductase were detected at 340 nm. Epalrestat was taken as the positive control. The inhibitory type, Ki and IC50 were determined by double reciprocal plot, quadratic drawing, and drawing of inhibitor＇s concentration to inhibitory ratio, respectively. Results： Epibueropyridinium A significantly inhibited the activity of aldose reductase in a competitive manner, with IC50 being 4.2 μg/ml and Ki being 4.88μg/ml. Conclusion.. Epibueropyridinium A is competitive inhibitor of aldose reductase.