Objectives: This experimental study was designed to investig:ue the effects of Oryungsan-gagampang on leptin and leptin receptor levels and differentiation of 3T3-L1 adipocyte. Methods: After 3T3-L1 adipocytes were incubated with various concentrations of Oryungsan-gagampang and Reductil(r) for 7 days, leptin and leptin receptor levels in 3T3-Ll adipocytes were measured by ELISA. To elucidate the mechanism of inhibitory effects of Oryungsan-gagampang on obesity, the 3T3-L1 adipocytes after oil red 0 staining were taken by digital photo system. Results: 1. Oryungsan-gagampang $1,000{mu}g/ml$ significantly increased leptin levels in 3T3-L1 adipocytes in comparison with the control group (p<0.05), and Oryungsan-gagampang 0.1 10, $1,000{mu}g/ml$ significantly increased leptin receptor levels in 3T3-L1 adipocytes in comparison with the control group (p<0.05). 2. Oryungsan-gagampang inhibited of differentiation of 3T3-L1 adipocytes. Conclusions: Oryungsan-gagampang showed significant effects on inhibiting differentiation of 3T3-Ll adipocytes, and increasing leptin levels and leptin receptor levels in 3T3-L1 adipocytes. Therefore, Oryungsan-gagampang could be used to treat obesity, but further studies are required.