Objectives: This study investigated the effects of water extract of Coix lacrymajobi var. mayuen on obesity and its associated factors in high fat diet (HFD) induced obese mice. Methods: Male C5BL/6 mice were randomly assigned to 4 groups, normal group (chow diet), a HFD, HFD with water extract of Coix lacrymajobi var. mayuen 100 mg/kg (W-Coix), and HFD with phentermine 5 mg/kg (Phen) as positive control. Body weight, food intake, fasting blood glucose were checked every week and then organs, blood serums were collected after 16 weeks of treatment. Results: Body weight and adipocyte size were significantly lesser in W-Coix than in HFD group; however energy efficiency in W-Coix were not different with HFD. The oral glucose tolerance test, serum glucose and insulin were significantly decreased in W-Coix, also lipid accumulations in liver tissue and lipid levels (total cholesterol, high density lipoprotein-cholesterol) were improved with W-Coix treatment. However skeletal muscle loss with HFD was not changed in W-Coix compared with HFD group. Conclusions: The W-Coix treatment decreased body weight, adipocyte size and it is associated with improved glucose and lipid metabolism. Further studies are needed to know the mechanism of antiobesity in W-Coix.