Abstract: To investigate the relationship between the protein expression of amplified breast cancer 1 ( AIB-1 ) and tamoxifen resistance in premenopausal patients with primary breast cancer. Methods: A total of 206 premenopausal patients with breast cancer were chosen for the study. The patients were diagnosed by pathology and were treated in The Fourth Hospital of Hebei Medical University. The estrogen and progestogen receptors as well as AIB-1 were analyzed by immunohistochemistry ( IHC ). All cases were divided into two groups: the group of ER or PR positive, in which patients accepted tamoxifen therapy ( treatment group, group T ) and the group of both ER and PR negative, in which no endocrine treatment was given ( control group, group C ). Group T and group C were divided into several subgroups according to their AIB-1 and HER-2 expression status. The disease-free survival ( DFS ) and overall survival ( OS ) rates were analyzed using Kaplan-Meier methods. Results: All cases were followed up from 30 months to 84 months, and the mean time was 65 months. A total of 58 patients experienced local recurrence and metastasis, while 36 of them died. The DFS and OS of 5 years were 71.84% ( 148/206 ) and 82.52% ( 170/206 ), respectively. High AIB-1 expression was correlated with the histologic grade 3, axillary lymph nodes metastases and over-expression of HER-2 ( χ2 = 12.573, P = 0.002; χ2 =7.939, P = 0.005; χ2 = 4.502, P = 0.036). The DFS and OS in the subgroup of both AIB-1 and HER-2 over-expression were lower than that of the other subgroups ( χ2 = 5.900, P = 0.002; χ2 = 4.533, P = 0.049 ), and the survival was lower than that of the other subgroups ( Log-rank test, χ2 = 8.903, P = 0.005; Log-rank test, χ2 = 9.405, P = 0.004 ). Conclusion: High AIB-1 is correlated with worse clinical biological behavior and prognosis. HER-2 over-expression, as well as high AIB-1 resulted in tamoxifen resistance for premenopausal patients with primary breast cancer. This condition implies that high AIB-1 may be an independent predictive factor of improved response to tamoxifen and may not be a factor that can predict tamoxifen resistance.