The high metabolic requirements of cancer cells result in excess accumulation of H⁺ in the tumor microenvironment. Therefore, the extracellular pH of solid tumors is acidic, whereas the pH of normal tissues is more alkaline. The acidic tumor environment is correlated with tumor metastasis, immune escape, and chemoresistance, but the underlying mechanisms remain elusive. Herein, we demonstrate that sodium bicarbonate, a weakly alkaline compound, induces cytotoxicity in ovarian cancer cells and hinders cancer migration and invasion in vitro. The anti-cancer efficacy of Olaparib can be significantly augmented when combined with sodium bicarbonate. In vivo experiments suggest that the combinatorial treatment of sodium bicarbonate and Olaparib is biocompatible and more effective at inhibiting ovarian cancer growth than either treatment alone. Additionally, RNA-sequencing results reveal that the differentially expressed genes are enriched in pathways related to reactive oxygen species (ROS) generation, such as the cGMP/PKG pathway. The combined treatment increases M1 macrophage composition in tumors and reduces the accumulation of excessive ROS. These findings strongly suggest that sodium bicarbonate holds great potential as an adjuvant treatment by scavenging ROS accumulation and promoting M1 macrophage composition, thereby enhancing Olaparib’s anti-cancer activity.