Resveratrol, a phytoallexin, has recently been reported to slow aging by acting as a sirtuin activator. Resveratrol also has a wide range of pharmacological effects on adipocytes. In this study, we investigated the effects of resveratrol on adipogenesis and apoptosis using 3T3-L1 cells. In mature adipocytes, 100 and 200 μM resveratrol decreased cell viability dose-dependently by 23 ± 2.7%, and 75.3 ± 2.8% (p < 0.0001), respectively, after 48 h treatment, and 100 μM resveratrol increased apoptosis by 76 ± 8.7% (p < 0.0001). Resveratrol at 25 and 50 μM decreased lipid accumulation in maturing preadipocytes significantly by 43 ± 1.27% and 94.3 ± 0.3% (p < 0.0001) and decreased cell viability by 25 ± 1.3% and 70.4 ± 1.6% (p < 0.0001), respectively. In order to understand the anti-adipogenic effects of resveratrol, maturing 3T3-L1 preadipocytes were treated with 25 μM resveratrol and the change in the expression of several adipogenic transcription factors and enzymes was investigated using real-time RT-PCR. Resveratrol down-regulated the expression of PPARγ, C/EBPα, SREBP-1c, FAS, HSL, LPL and up-regulated the expression of genes regulating mitochondrial activity (SIRT3, UCP1 and Mfn2). These results indicate that resveratrol may alter fat mass by directly affecting cell viability and adipogenesis in maturing preadipocytes and inducing apoptosis in adipocytes and thus may have applications for the treatment of obesity. Copyright © 2008 John Wiley & Sons, Ltd.