Pinusolide and its derivative, 15-methoxypinusolidic acid (15-MPA) are diterpenoid compounds isolated from Biota orientalis, which has been used as a Korean folk medicine for treating inflammatory disorders. Pinusolide and 15-MPA suppress nitric oxide generation by suppressing inducible nitric oxide synthase and exerted anti-inflammatory functions, whereas other functions and regulatory mechanisms are largely unknown. In this study, we investigated whether pinusolide and 15-MPA modulate adipocyte differentiation from pre-adipocytes 3T3-L1 cells. We found that 15-MPA, not pinusolide, suppressed adipocyte differentiation in a dose-dependent manner, as revealed by lipid droplet formation and expression of adipogenic genes such as adiponectin and aP2. 15-MPA did not affect mRNA and protein levels of PPAR${gamma}$, a key adipogenic transcription factor, whereas transcriptional activity of PPAR${gamma}$ was significantly attenuated by 15-MPA. While aP2 promoter activity was increased by ectopic overexpression of PPAR${gamma}$ or by rosiglitazone-induced endogenous PPAR${gamma}$ activation, PPAR${gamma}$-induced aP2 promoter activity was inhibited in the presence of 15-MPA. These results suggest that 15-MPA suppresses adipocyte differentiation through the inhibition of PPAR${gamma}$-dependent adipogenic gene expression.