Tumor-associated macrophages (TAMs) are abundant in the tumor microenvironment and typically exhibit pro-tumoral phenotypes. TAMs overexpress the signal regulatory protein alpha (SIRPα) receptor on their surface, which interacts with CD47 on tumor cells to inhibit their phagocytic activity. In this study, we developed lipid nanoparticles modified with an anti-SIRPα antibody (aSIRPα) for the targeted delivery of microRNA-155 (miR155@aSIRPα-LNP) to TAMs, aiming to enhance their anti-tumoral phenotypes within the tumor microenvironment. The aSIRPα modification not only facilitated nanoparticle uptake by TAMs rather than B16F10 cells, but also blocked the anti-phagocytosis signal by disrupting the interaction between SIRPα and CD47 on cancer cells. This dual functionality enhanced the expression of anti-tumoral phenotype markers in TAMs and activated macrophage-mediated phagocytosis of tumor cells. In a melanoma model, intratumoral administration of miR155@aSIRPα-LNP to B16F10 tumor-bearing mice reprogrammed TAMs toward anti-tumoral phenotypes. The anti-tumoral cytokines released by these TAMs remodeled the immunosuppressive tumor microenvironment, increasing cytotoxic T cell infiltration and reducing the regulatory T cell population, inhibiting tumor progression. This approach indicates the potential of miRNA-based therapies to overcome the limitations of current immunotherapies in treating cold solid tumors. Overall, the results suggest that delivering miR155 to TAMs by targeting SIRPα is a promising strategy for modulating the immunosuppressive tumor microenvironment in cancer immunotherapy.