Bark extract of Populus nigra was examined as a possible inhibitor of aldose reductase, a key enzyme involved in diabetic complications. The aqueous acetone extract of P. nigra was subjected to gel filtration chromatography to produce an active compound, populoside, which inhibited aldose reductase with 50% inhibitory value of $18.55;{mu}M$ in a non-competitive manner. Populoside also inhibited sorbitol accumulation by 48.84% at $50;{mu}M$. These results suggested that the P. nigra-derived component populoside has the potential to be used in the treatment of diabetic complications.