Zingiber cassumunar (ZC) is used by tribal people in northern Thailand in traditional remedies for antiobesity and in food recipes. Extracts from this plant have been studied for several pharmacological effects including anti-obesity, but with no clear evidence on cellular mechanism of activity. This study aim to investigate the lipolytic and anti-adipogenic activity of crude extracts from ZC on in vitro cultures of the mouse adipocyte cell-model, 3T3-L1. Dry rhizome powder was extracted with absolute ethanol and boiled-water. On the exposed pre-adipocytes to the extracts, cytotoxicity was not detected by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Lipid content and glycerol release were assessed using Oil Red-O and a commercial Adipolysis Assay kits respectively. The extracts exhibited no significant lipolytic activity on the exposed mature-adipocytes, in serial dilutions ranging from 1 to 800 mg/ml. However, anti-lipogenic activity was presented. All extracts significantly reduced the lipid content of exposed differentiating-adipocytes. This anti-lipogenic activity was confirmed by the expression of selected genes, determined by using real-time PCR techniques, in four groups namely: adipocyte differentiation genes, glucose uptake genes, lipid metabolism genes and fatty acid oxidation genes. 1 H NMR spectrum of the extracts exhibited the prominent olefinic protons of phenylbutanoids, the group of compounds previously proved with several bioactivities. This study provided evidences of mechanisms that apparently verify the traditional use of ZC to prevent obesity.