Inhibitory effects of the whole extract and isolated compounds from the leaves of Vaccinium koreanum (Ericaceae) on rat lens aldose reductase (RLAR) and on platelet aggregation were investigated for the prevention or the treatment of chronic diabetic complications. Arbutin, isolated from n-butanol fraction of methanol extract, exhibited a potent inhibitory effects on rat platelet aggregation induced by ADP $(IC_{50}=0.12;{mu}M)$ and collagen $(IC_{50}=0.039;{mu}M)$ and showed same inhibitory activities with positive control, tetramethylene glutaric acid, on RLAR.