This study examined how dietary flavonoids, including catechin, quercetin and kaempferol, affect the differentiation of 3T3-L1 adipocytes. Eight days following induction for differentiation with MDI medium and simultaneously with the tested flavonoids (day 8), our study found significantly reduced (p < 0.05) intracellular triacylglycerol accumulations of 3T3-L1 cells. This compared positively against the smaller reduction in accumulation found in the vehicle control. This suppressing effect was found to be dose-dependent, and a 54.4%, 45.7% and 29.9% decrease of triacylglycerol production was observed for catechin, quercetin and kaempferol (25-100 μM), respectively. Additionally, RT-PCR assays demonstrated that catechin, quercetin and kaempferol markedly reduced the mRNA expressions of C/EBP-α, PPAR-γ and SREBP-1, which are key transcription factors for 3T3-L1 adipogenesis. These results suggest that dietary flavonoids suppress 3T3-L1 differentiation by down regulating adipogenic transcription-factors. Further study recommended to explore the potential health benefits of catechin, quercetin and kaempferol in the control of body weight.