Saponin from Ophiopogon japonicus was isolated and preliminary identified by physical and chemical methods. The antioxidant and macrophages-modulating activities of the saponin were also investigated employing various established systems in vitro. The results of physical-chemical identification indicated that saponin was steroidal saponin. It was observed that the scavenging activity of saponin on 2, 2-diphenyl-1-picry-hydrazyl (DPPH) significantly increased in a concentration-dependent manner. The scavenging rate of it on DPPH radical was 99.64% when the concentration of the saponin was up to 5 mg/ml. For scavenging hydroxyl radical, it first increased and then decreased gradually with the increase of concentration, and reached the strongest scavenging rate at the concentration of 2 mg/ml. Saponin also exhibited prominent macrophages-modulating activity by the promotion of phagocytic capacity, macrophage viability, nitric oxide (NO) production and interleukin-1 release. It follows that saponin from O. japonicus can be explored as a novel and potential natural antioxidant and immunostimulants. Key words: Ophiopogon japonicas, saponin, antioxidant activity, macrophages.