Obesity is a worldwide problem that contributes to serious diseases, including diabetes, hypertension, and atherosclerosis. Recently, much research has examined functional natural materials and their anti-obesity activity. This study investigated the effect of enzyme-treated Ecklonia cava extracts on mice fed a high fat diet. To test the anti-obesity effects of a diet containing the enzyme-treated E. cava extracts (EEc), C57BL/6NTacSam mice were divided into six groups : normal diet (ND), high-fat diet (HFD), high-fat with Garcinia extract diet (GHD), and three high-fat with EEc diet (EHD250, EHD500, and EHD1000) groups. After 9 weeks, body weight was increased significantly in the HFD group compared to all of the EHD groups, and the weights of the liver, perirenal fat and epididymal fat paralleled the increase in body weight. The serum GOT, GPT, triglyceride, total cholesterol, and LDL-cholesterol levels were lower in the EHD1000 group than in the HFD group. The glucose and leptin concentrations were lowest in the EHD1000 group and C/EBP family expression was decreased in a dose-dependent manner. These results indicate that E. cava extracts not only have anti-oxidation functions but also anti-obesity effects.