Studies show nutrition effects on function and histology of the brain. Based on our search, there is no study on the effects of Ceratonia siliqua on dark neurons in the brain. Therefore, this study investigated the effects of different doses of carob extract on the dark neurons in hippocampus of adult male Balb/c mice. In this experimental study, 32 adult male Balb/c mice were randomly divided into five groups (sham and carob 1 to 3). Carob 1 to 3 groups received intraperitoneally doses of 200 mg/kg, 400 mg/kg and 800 mg/kg of carob extract for 14 days. Then, the brains were stained with toluidine blue and the mean density of the dark neurons was counted in the hippocampus. SPSS software and one-way ANOVA was used to analyze the data. The mean number of dark hippocampal neurons was 64.71 ± 1.68 N/mm2 in sham group and 68.71 ± 0.9 N/mm2 in carob 1 group. Statistical analysis showed the administration of 200-800 mg/kg of carob extract does not change the number of dark neurons in the hippocampus of the adult mice compared to the sham group.