Background: Fluid shear stress (FSS) is a biomechanical force that can produce phenotypic changes in the cells that are directly in contact with the flow of fluid. Accumulating evidence indicates high FSS to possess the potential ability to prevent tumor development and suppress cancer growth. However, the exact mechanism of its antitumorigenic effects is still not clear. Objective: In this study, we aimed to investigate the effect of FSS on breast cancer microenvironment via macrophage modulation. Methods: We exposed THP-1 like-macrophages to different levels of FSS. The supernatant from THP1-like-macrophages after exposure to FSS was used as conditioned medium (FSS-CM). Subsequently, we analyzed human breast cancer cells, MCF-7, and endothelial cells, as well as HUVECs cultured with FSS-CM. Results: Study outcomes have demonstrated that low FSS-CM inhibited apoptosis as well as induced tumor migration in MCF-7 cells. Conversely, high FSS-CM promoted apoptosis, inhibited tumor migration, and induced G1-phase arrest in MCF-7 cells. Furthermore, low FSS-CM was found to promote proliferation of HUVECs. Conclusions: In conclusion, this study highlights the complex interplay between FSS and cancer cell behavior. Our findings provide in vitro evidence that high FSS exerts an anti-cancer effect by promoting THP-1-like macrophage polarization toward an anti-tumor phenotype, leading to increased apoptosis and reduced migration in MCF-7 cells. These results suggest that the modulation of macrophage polarization may underlie the therapeutic potential of high FSS in suppressing breast cancer progression.