Many studies have demonstrated that plant extracts possess various biological and pharmacological properties including immunomodulatory activity. Caesalpinia volkensii Harm (Caesalpiniaceae), a medicinal herb native to Kenya was investigated for its immunomodulatory effects.Ethanolic, methanolic and aqueous extracts of the plant was prepared and administered orally in normal albino rats at different concentrations. The effect of C. volkensii on various immunological parameters such as neutrophil adhesion, phagocytosis, nitroblue tetrazolium reduction (NBT) test and macrophage phagocytosis was assessed. The effect of C. volkensii on in vivo cell mediated immunity was also measured by delayed type hypersensitivity (DTH) reaction.The percentage neutrophil adhesion for extract treated animals with 125 to 1000mg/kg of the extracts ranged from 13.3% to 42% showing a significant stimulatory activity. Phagocytic index (PI) for animal treated group was significantly enhanced(P<0.001). NBT reduction test as well as macrophage phagocytosis revealed that in animal treated groups, these were significantly enhanced. In DTH skin test, the mean footpad thickness of all rat groups treated with 125, 250, 500 and 1000mg/kg of the extract at 24 hr after immunization with antigen was 3.5+0.6mm compared to 2.5+0.5mm for the non treated group.Results of this study showed the ability of C. volkensii extract to strengthen and stimulate the innate immune system and enhance cellular immune response.