Funoran (an algal polysaccharide from Gloiopeltis tenax) significantly inhibited the growth of Ehrlich ascites carcinoma and solid Ehrlich, Meth-A fibrosarcoma, and Sarcoma-180 tumors. In tumor-bearing mice, funoran significantly induced the enhancement of delayed-type hypersensitivity response to sheep red blood cells. When given intraperitoneally, funoran increased the spleen weight of mice. Morphological observations indicated that funoran augmented the transformation from lymphocytes to plasma cells in the spleen. In addition, changes in the T-cell subsets in the spleen, thymus, and peripheral blood were measured by flow cytometry. The results showed that the percentages of L3T4+ and Lyt 2+ T-cells were markedly increased in the peripheral blood. The percentages of asialo CM1+ cells in the thymus and peripheral blood were also significantly increased. Our results suggest that the antitumor effect of funoran is related to the augmentation of T-helper, T-cytotoxic, and NK cells.