Aldose reductase (AR) is well known as a key enzyme in the polyol pathway to catalyze the reduction of glucose to sorbitol, and the intracellular accumulation of sorbitol has been implicated in the chronic complications of diabetes such as cataract (Yoshikawa et al., 2002). Thus, AR inhibitors may offer the possibility of preventing or arresting the progression of these long-term diabetic complications (Manzanaro et al., 2006). In order to discover AR inhibitors from natural sources, compounds 1–4 were evaluated in vitro for their inhibitory activity against AR. Compound 1 showed moderate inhibitory activity, with an IC50 value of 1.63 μM, while the positive control, epalrestat, had an IC50 value of 1.88 nM. The finding of this investigation was the ability of 1 to inhibit AR in vitro. Further in vivo studies are needed to establish 1 as potential agent for the prevention and treatment of diabetic complications.