This study was to investigate the effect of high-fat diet on macrophage immunocompetence in C57BL/6 mice. C57BL/6 male mice (4 weeks aged, n=16) were divided into two groups. HD groups fed high-fat diet (45% of fat) and ND groups fed chow diet (10% of fat). Peritoneal macrophages were obtained from each mouse intra-peritoneal by sterile lavage method. Macrophage were stimulated with $1{mu}g/ml$ of lipopolysaccharide (LPS) for 24 hr. Body weight was significantly increased by high-fat diet. Macrophage phagocytosis of HD was significantly lower than that of ND. After 24 hr of LPS stimulation, NO, IL-$1{eta}$ and IFN-${gamma}$ production of HD were significantly lower than those of ND. There were no significant differences in the production of TNF-${alpha}$ and IL-12 between HD and ND. These findings suggest that high fat diet-induced obesity is associated with decreased Immunocompetence and antigen-stimulated sensitivity of peritoneal macrophage, and lower production of NO, IL-$1{eta}$ and IFN-${gamma}$ may contribute to these changes.