Abstract: The effects of Dunaliella salina (EDS) on tumor immunity were observed in mice.The results revealed that in high and medium doses of EDS significantly (P<0.05)enhanced proliferative response to Con A of spleen cells and tumor necrosis factor activity produced by peritoneal macrophage not only in normal mice，but also in tumor-bearing mice.In addition，EDS could markedly reduce spontaneous pulmonary metastases of Lewis lung carcinoma (P<0.05)compared to the control group.These findings suggested that antitumor action by oral administration of EDS may be due to improving antitumor immunity.