Semaglutide, a glucagon-like peptide 1 receptor agonist, is an antidiabetic that has recently shown promising immunomodulatory and antitumor effects. Breast cancer is the most common type of cancer affecting women worldwide. The aim of this study was to analyze the effects of semaglutide on the antitumor immunity in a 4T1 mouse breast cancer model. After induction of breast cancer, BALB/C mice were treated intraperitoneally with semaglutide. Semaglutide administration decelerated tumor appearance, growth and progression. The antidiabetic drug showed neither a direct cytotoxic effect in vitro, nor an angiogenic effect. Furthermore, depletion of NK cells had no affect on tumor growth in semaglutide treated mice suggesting a non-NK cell-dependent mechanism. However, semaglutide increased the accumulation and maturation of CD11cdendritic cell, while decreasing the percentage of FoxP3regulatory T cells in the spleen and primary tumor. In addition, semaglutide increased tumor infiltration and promoted the antitumor phenotype of T cells, in vivo. Furthermore, semaglutide enhanced the cytotoxic capacity of CD8T cells, in vitro. These results suggest that semaglutide enhances the acquired antitumor immune response and has potential for the future treatment of malignancies.