The effects of citrus flavonoids, hesperidin and naringin, on the lipid metabolism were investigated in cultured human hepatocyte HePG2 cells. HepG2 cells were cultured for 6 h and 24 h to the control medium or the media containing hespridin and narigin, which concentrations were 0.5 and 5.0 mg/$mell$. There were no significant effects on cell proliferation and cellular protein content, except for increased in these parameters by adding both citrus flavonoids (0.5 mg/$mell$). The cellular content of triacylglycerol after 6 h incubation with 0.5 mg/$mell$ hesperidin and naringin was markedly increased, and after 24 h incubation that was decreased in both citrus flavonoids supplementation. The supplementation of 5.0 mg/$mell$ hesperidin caused a marked decrease in the cellular cholesterol content following 6 h incubation, and that was also reduced markdly, in a dose-dependent manner, during incubation for 24 h. However, there was no significant difference in the cellular cholesterol content in medium supplemented with naringin. The effect of hesperidin and naringin on acyl-CoA: cholesterol acyltransferase (ACAT) activity was studied in vivo and in vitro. The data confirmed that hesperidin inhibit ACAT activity in vivo and in vitro, whereas naringin had no such effect on ACAT activity in vivo but not in vitro. The present study suggests that hesperidin reduces the cellular triacyglycerol and cholesterol contents in human hepatocyte HepG2 cells.