Garlic extracts exert anti-cancer and anti-inflammatory effects. However, the anti-adipogenic effect of garlic-derived compounds remains unclear. In this study, we examined the effect of thiacremonone, a sulfur compound isolated from garlic, on adipocyte differentiation using 3T3-L1 cells. We found that thiacremonone significantly inhibited 3T3-L1 differentiation via down-regulation of adipogenesis-related transcription factors and adipogenic markers. The inhibitory effect mainly occurred at the early phase of differentiation in 3T3-L1 cells. There was no cytotoxic effect of thiacremonone in 3T3-L1 cells and treatment of differentiating 3T3-L1 cells with thiacremonone resulted in AMPK activation, which led to an attenuated expression of acetyl CoA carboxylase-1 (ACC-1), an essential enzyme for the synthesis and usage of fatty acids. Moreover, thiacremonone enhanced the mRNA level of carnitine palmitoyltransferase (CPT-1). The modulating effect of thiacremonone on expressions of genes involved in lipolysis was partially abrogated by treatment with compound C, an AMPK inhibitor. Taken together, these results indicated that thiacremonone-induced AMPK activation, inhibition of ACC-1 expression and concomitant recovery of CPT-1 expression resulted in the suppression of intracellular lipid droplet levels, suggesting that thiacremonone may induce reduction of lipid synthesis and increases in fatty acid oxidation partially mediated via AMPK activation. Thiacremonone may be a promising compound for the treatment of obesity., (Copyright © 2012 Elsevier Inc. All rights reserved.)