Semaphorin4A (Sema4A) is a family member of semaphorins expressed in immune cells and is also related with disease progression of tumor disease. In this study, we investigate the expression and pathological role of Sema4A in breast cancer (BCa). Our data showed that the expression of Sema4A increased in the tissues and serum of BCa patients when compared with normal controls. The expression of Sema4A in BCa cells could be induced by hypoxic treatment, whereas silencing hypoxia-inducible factor (HIF)-1α could attenuate the above induced. Furthermore, chromatin immunoprecipitation (ChIP) analysis demonstrated that HIF-1α could regulate the expression of Sema4A through directly binding to the promoter of Sema4A gene, whose enrichment could be further enhanced by hypoxic stimulation. In addition, silencing Sema4A could inhibit the proliferation, vascular endothelial growth factor (VEGF) production and the phosphorylation of Akt, extracellular signal-regulated kinase (ERK)1/2 mitogen-activated protein kinase (MAPK) and signal transduction and activator of transcription (STAT)3, but induce apoptosis of BCa cells in the presence of hypoxia. In contrast, recombinant human Sema4A treatment showed the opposite effects. Taken together, these results suggest that Sema4A could promote progression of BCa in the presence of hypoxia and it may hold potential for treatment target for BCa.