The MeOH extract of Rhus verniciflua heartwood inhibited lipid accumulation in 3T3-L1 adipocytes. Chromatographic methods including of silica gel, RP-18 and high-pressure liquid chromatography isolated sulfuretin and fisetin from the extract as active constituents. The isolated compounds, especially sulfuretin, strongly inhibited lipid accumulation in adipocytes. The treatment of sulfuretin and fisetin led to decreased expression of peroxisome proliferator-activated receptor-gamma ($PPAR{gamma}$), as an important transcription factor in fat cell differentiation, which was equal to the decrease in the quercetin positive control. The presence of a hydroxyl group (C-5) in quercetin compared to fisetin, and the presence of C-2 double bonds in fisetin compared with fustin increased the inhibitory effect of lipid accumulation.