BACKGROUND: Chemotherapy-induced immunosuppression significantly impacts patient's quality of life. Umbelliferone (UMB) is known for its anti-inflammatory, antioxidant, and anti-apoptotic properties, but its effects on cyclophosphamide (CTX)-induced immunosuppression need further study. METHODS: We established a CTX-induced immunosuppressed mouse model and administered varying doses of UMB. Immune function was assessed by evaluating white blood cells, lymphocytes, thymus and spleen indices, and CD4+/CD8+ T cell ratios. Serum levels of IL-2, IFN-γ, IgA, IgM, and IgG, along with macrophage phagocytic activity, NK cytotoxicity, and lymphocyte proliferation, were measured. Untargeted metabolomics was used to identify key pathways regulated by UMB, and RT-qPCR and Western blotting were performed to analyze the expression of related enzymes and metabolites. RESULTS: UMB intervention increased white blood cells, lymphocytes, thymus and spleen indices, and CD4+/CD8+ T cell ratios in CTX-immunosuppressed mice. It reversed reduced levels of serum IL-2, IFN-γ, IgA, IgM, and IgG and improved macrophage phagocytic activity, NK cytotoxicity, and lymphocyte proliferation. Key pathways identified by metabolomics included histidine and purine metabolism. UMB improved levels of histamine, L-glutamate, L-aspartate, xanthine, dAMP, deoxyinosine, xanthosine, and cGMP and upregulated HDC, ASPA, and PNP while downregulating XDH, PDE5, ROS, and MDA in spleen tissue. UMB enhanced SOD activity and GSH levels and reduced apoptosis, as indicated by lower TUNEL-positive expression. CONCLUSION: UMB enhanced immune function in CTX-immunosuppressed mice through the regulation of histidine and purine metabolism, exhibiting antioxidant and anti-apoptotic effects. These findings highlight the potential of UMB in mitigating immunosuppression.