The oral administration of Aurantii nobilis pericarpium (ANP) extract and Aurantii immaturi pericarpium (AIP) extract suppressed the cell viability of both thymocytes and splenocytes in BALB/c mice. The ANP extract (500 mg/kg) enhanced the population of $B220^+$ cells, and the AIP also enhanced the population of B220+ and Thy-1+ cells in splenocytes. The AIP extract enhanced the population of $CD4-CD8^+$ cells in splenic T-lymphocytes. However, the ANP did not affect, whereas the AIP enhanced the phagocytic activity and the nitric oxide production in peritoneal macrophages.