Zingiber officinale Roscoe commonly known as ginger, has been used in traditional medicine. Inhibtion effect of galanolactone isolated from Z. officinale Roscoe on adipogenesis in 3T3-L1 cells was evaluated. Effect of galanolactone on 3T3-L1 adipocyte differentiation was measured by Oil Red O staining, and cytotoxicity effect of galanolactone was analyzed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. The expression of various genes involved in adipogenic action of galanolactone was determined by real-time PCR and Western blot. Peroxisome proliferator-activated receptor ${gamma}$ ($PPAR{gamma}$) luciferase transactivation assay was used to evaluate the $PPAR{gamma}$ transcriptional activity of galanolactone in HEK 293T cells. Galanolactone inhibited lipid accumulation and expression of adipocyte fatty acid-binding protein (aP2) and resistin in a dose-dependent manner in 3T3-L1 cells. Treatment with 50 and 100 ${mu}M$ of galanolactone significantly decreased the troglitazone-induced $PPAR{gamma}$ transcripitional activity in HEK 293T cells, and suppressed expressions of $PPAR{gamma}$ and CCAAT-enhancer-binding protein ${alpha}$ ($C/EBP{alpha}$) at mRNA and protein levels in 3T3-L1 cells. These findings suggest that galanolactone isolated from Z. officinale Roscoe exerts anti-obesity effect through downregulation of adipogenic transcription factors and adipogenic marker genes.