Semaphorin 3A (SEMA3A) is a canonical secreted member of the class 3 semaphorin family, the largest subfamily of the semaphorin superfamily with conserved sema domains. It exerts biological functions primarily by binding to neuropilin-1/plexin-A receptor complexes, acting as a key axon guidance cue in neural development. SEMA3A potently inhibits cell proliferation and migration in multiple cell types including neurons, endothelial and cancer cells; it also induces caspase-dependent apoptosis in tumor cells and suppresses angiogenesis. Additionally, it modulates immune cell trafficking, playing critical roles in neural patterning, tissue morphogenesis and cancer progression.Thus, chemotaxis assay used 24-well microchemotaxis system was undertaken to detect the chemotactic effect of SEMA3A on MDA-MB-231. Briefly, MDA-MB-231 cells were seeded into the upper chambers and SEMA3A at different concentrations was added in lower chamber with a polycarbonate filter(8um pore size) used to separate the two compartments. After incubation at 37℃ with 5% CO2 for 1h, the filter was removed,then cells in low chamber were observed by inverted microscope at low magnification . Result shows that SEMA3A is able to induce migration of MDA-MB-231 cells. The migrated MDA-MB-231 cells in low chamber at low magnification were shown in Figure 1.