Abstract: Objective: To detect expression of P-gp and LRP and to determine if a correlation exists between these expression levels and the prognosis of bilateral primary breast cancer (BPBC). Methods: The expression levels of P-gp and LRP were studied in 45 cases with BPBC and 41 cases with unilateral primary breast cancer (UPBC) using immunohistochemistry, and the relationship between the expression of these two proteins and survival time of the patients with BPBC was analyzed. Results: The difference in P-gp overexpression between the patients with the first tumor of BPBC and the UPBC was statistically significant (P<0.05). The difference in LRP overexpression between the patients with first tumor of BPBC and the UPBC was also statistically significant (P<0.05). There was no correlation between the expression of P-gp and LRP and the histological grade, tumor size or pathological type, but there was a correlation between the expression and clinical stage of BPBC. There was also a relationship between the expression of P-gp in the second tumor of BPBC and the relapse and metastasis of the BPBC, but there was no relationship between various expression patterns of P-gp and LRP and survival time of BPBC. Conclusion: P-gp and LRP might be related to pathogenesis of BPBC and may become a prognostic factor and for high-risk BPBC.