Abstract: To study the immunomodulatory effects and safety of an antioxidant dietary supplement (AS) composed primarily of Haematococcus pluvialis, selenium-enriched yeast, propolis extract, and vitamin E. Three different dosages (0.1, 0.2, and 0.4 g/kg bw) were administered via gavage once daily for 30 days in mice. The impact of this antioxidant dietary supplement was observed on various parameters, including spleen index, thymus index, splenic lymphocyte transformation activity, delayed-type hypersensitivity, antibody-producing cell levels, hemolytic complement 50 (HC₅₀), carbon clearance rate, phagocytic activity of macrophages, and natural killer cell activity. The potential carcinogenicity of the test materials, and their genotoxic effects on cells and the reproductive system were assessed through the Ames test, bone marrow micronucleus assay, and mouse sperm abnormality test, respectively. Subacute toxicity was investigated through a 30 day feeding trial. Results showed that compared to the control group, the middle and high-dosage groups exhibited significant increases in OD difference by 10.32% (P<0.05) and 14.29% (P<0.01), respectively. It indicated that the AS promoted lymphocyte proliferation and transformation capacity in mice. In the high-dosage group, the difference in ear swelling between the left and right ears increased by 8.02% (P<0.05), and the number of hemolytic plaques increased by 22.12% (P<0.05). It suggests that the AS significantly improved delayed-type hypersensitivity and antibody-producing cell capacity. Importantly, no acute toxicity, genotoxicity, or subacute toxicity were observed. It is demonstrated that the AS is safe for consumption and significantly enhances immunity.