Polyphenolic compounds were examined for their effects on suppressing adipocyte differentiation in 3T3-L1 cells. Most polyphenolic compounds inhibited adipocyte development from 3T3-L1 cells to some extent. Among them, rutin was the most effective in suppressing adipocyte differentiation in a dosage dependant manner. Activity of glycerol-3-phosphate dehydrogenase (GPDH), which has a central position in lipogenesis in adipose cells, was also decreased by rutin addition at the induction stage. RT-PCR results demonstrated that mRNA expression of adipogenic transcription factors such as peroxisome proliferator-activated receptor-gamma (PPARgamma) and CCAAT/enhancer binding protein-alpha (C/EBPalpha) in 3T3-L1 cells were remarkably down regulated by rutin treatment. For further investigation on anti-adipogenic activities of rutin, it was orally administered (25 and 50 mg/kg b.w/daily) with high-fat diet (64.4% of total calories as fat) to C57BL/6 mice. Body weight gains were less in high-fat diet + rutin fed groups (HFR) than high-fat diet alone fed group (HF) after 4 weeks. Total cholesterol contents in blood were significantly lower in HFR groups. When mRNA expressions of PPARgamma and C/EBPalpha in hepatocytes were compared between the control HF and HFR groups, their expressions in hepatocytes of HFR groups were significantly suppressed. These results indicate that rutin inhibits adipogenic development in pre-adipocytes and hepatocytes by down regulating expressions of key adipogenic transcription factors.