BACKGROUND Grape seed extracts (GSE) are known to present health benefits such as antioxidative and anti-obesity effects in animal models. The purpose of this research is to determine whether the specially manufactured GSE, catechin-rich GSE (CGSE), can protect against obesity induced by a high-fat diet (HFD) and to address the mechanism underlying this effect. METHODS The componential analysis of CGSE was performed using liquid chromatography/mass spectrometry. Oxygen consumption and the respiratory quotient were determined using 500 mg/kg CGSE administered orally for 3 days in 14- to 15-week-old male C57BL/6J mice. Nine-week-old male C57BL/6J mice were supplemented with 0.5 or 1% CGSE in a HFD for 12 weeks, and their body weight and food intake were monitored. Blood and tissue samples were collected and analyzed. RESULTS The main polyphenol components of CGSE were catechin and epicatechin. CGSE supplementation in the HFD-induced obesity model chronically suppressed the increase in body weight and the weight of fat pads. Furthermore, CGSE improved metabolic parameter abnormalities and upregulated the fatty acid oxidation-related genes in the liver. CONCLUSIONS These findings suggest that CGSE contains monomeric catechins in high concentrations and ameliorates HFD-induced obesity in C57BL/6J mice.