Acorus gramineus is a herb used frequently in oriental medicine. Clinically, the effects of Acorus gramineus are known as awakening of one’s consciousness, removal of sputum, and relief of autism. Experimentally, Acorus gramineus root(AGR)-induced cerebral blood flow increase depending on the concentration causes diverse responses of blood pressure and regional cerebral blood flow and possesses strong inhibitory effects of apoptosis in the nervous system. We investigated the effects of AGR water extract on the adipose tissue status. Male C57BL/6 mice were fed high fat diet and a total of 35 mice were divided into 5 groups: normal group, control group, and groups treated with AGR water extract at concentrations of 20, 100, and 500 mg/kg. The mice were treated by oral administration once a day for consecutive 6 weeks, and their weight changes were monitored. As the results, the groups treated with AGR water extract showed weight loss. Also, the weights of liver, epididymal fat, retroperitoneal fat and peri-renal fat were decreased in the groups treated with AGR water extract. In histopathological examination, the sizes of adipose tissues decreased in liver, epididymal fat, retroperitoneal fat, and peri-renal fat. These results indicate that AGR water extract have an anti-obesity activity, which could be used as an useful material to decrease body adipose tissues.