Objectives : The researcher investigated the anti-obesity effect of Alismatis Orientale Rhizoma(AP) water extract in mice fed a high fat diet and focused on the analysis of local area adipose tissue. Methods : Male ICR mice were divided into three groups, which were fed either a normal AIN diet, a 45% high fat diet (CT group), or a high fat diet and orally administration with a concentrations of 100 mg/kg (AP100 group) and 300 mg/kg body weight (AP300 group) for eight weeks. Results : As compared with CT group, AP100 group showed significant reductions in absolute weight of liver. As compared with CT group, AP100 group and AP300 group showed significant reductions in weight gain and relative weight of total fat. AST, triglyceride, total-cholesterol levels from the AP 100 group and 300 group were significantly lower than those of the CT, and ALT, LDL-cholesterol levels from the AP 100 group was significantly lower than those of the CT. But serum HDL-cholesterol levels from the AP 100 group and 300 group were significantly higher than those of the CT. And serum adiponectin levels from the AP 100 group was significantly higher than those of the CT. In result of real time PCR, all mRNA expression(PEPCK, G6Pase, PGC-$1{alpha}$ and $ERR{gamma}$) of two experimental groups were significantly decreased compared to those of CT group. The treatment with AP on local abdominal area made a fat cell size lessen on the fat tissue in the abdominal cavity and subcutaneous area. Conclusions : These results suggest that AP has an anti-obesity effect and the effect is mediated by inhibition of fat gain.