Mice homozygous for the lethal autosomal recessive anorexia mutation (anx) present with premature death around postnatal day 22. The anorexia mutant mice also present phenotypes such as reduced body weight, decreased food intake, and abnormal behavior characteristics such as body tremors, hyperactivity, uncoordinated gait, and head weaving. In order to investigate the expression of c-Fos in the hippocampus of anorexia mutant mice, the immunohistochemistry was performed in this study. The anorexia mutant mice exhibited lower expression of c-Fos in the hippocampus regions thBn the control group. In the CA3 and dentate gyrus, the number of c-Fos-positive cells in anorexia mutant mice was noticeably lower than that in control mice. However, no significant difference was found in the number of c-Fos-positive cells in CA1 of the two groups. The result suggests that the phenotypic characteristics of anorexia mutant mice may be associated with the hippocampal deficits of c-Fos expression.