Abstract: AimTo study the biological effect and molecular mechanism of neotoralactone on lipid metabolism in HepG2 cells. MethodsAnimal experiments were carried out to examine the biological effects of the compound. Differentiation assay was carried out to determine the effect of the compound on the 3T3L1 preadipocyte. Finally, a highdensity cDNA microarray containing about 10 000 human genes and ESTs were used to analyze the gene expression profiles of the HepG2 cells with and without neotoralactone treatment. Results Preliminary results showed that neotoralactone can decrease the increase of body weight of rats fed with high nutrient diet. As the differentiation assay showed that neotoralactone has minimal effect on the obese 3T3-L1 preadipocyte cell line, HepG2 heptocarcinoma cell line was used as the model system because one of the proposed mechanisms of weight reduction effect of Cassia obtusifolia is the alteration of lipid metabolism primarily taken place in the liver. The results showed that neotoralactone regulates a panel of genes related to lipid metabolism. ConclusionThe effects of neotoralactone may be due to the regulation of a panel of important genes related to lipid metabolism.