Objective To investigate the expression of hypoxia inducing factor 1 alpha (HIF-1α) in human breast cancer and its relationships with microvessel density （MVD）, proliferating cell nuclear antigen (PCNA) protein, other tumor biomarkers and clinicopathologic factors. Methods Immunohistochemical staining (SP) was used to measure the expressions of HIF-1α and PCNA in human breast fibroadenoma, usual hyperplasia and adenocarcinoma, and the MVD was determined by anti-CD34 immunostaining. Results No HIF-1α was observed in the lesions of breast fibroadenoma and hyperplasia. However, the positive expression rate of HIF-1α in the ductal carcinoma in situ （DCIS） was 55.0% (11/20) and the infiltrative breast cancer was 85.0%(51/60). The total high expression rate of PCNA in breast cancer was 75.0% (60/80), in which the rate of DCIS counted for 65.0% (13/20) and the rate of infiltrative adenocarcinoma counted for 78.3% (47/60). There were positive correlations between the expresson of HIF-1α and the expression of PCNA (r=0.693， P＜0.01) and MVD in DCIS (r=0.682, P＜0.05), respectively, but there was no relation between HIF-1α and MVD in infiltrative breast cancer. The expression of HIF-1α was associated with tumor cell proliferation, lymph node metastasis, estrogen receptor status (P＜0.01). Conclusion The expression of HIF-1α increased in breast cancer and it is associated with tumor cell proliferation, lymph node metastasis, estrogen receptor status. Thus, HIF-1α may play an important role in the tumor cell proliferation, vasiformation, progression and metastasis of breast cancer, and may become a new target for tumor treatment.