Objective: To explore the effects of postmastectomy radiotherapy (PMRT) on the locoregional failure-free survival (LRFFS) and overall survival (OS) of breast cancer patients under different tumor stages and with one to three positive axillary lymph nodes (ALNs). Methods: We conducted a retrospective review of 527 patients with one to three positive lymph nodes who underwent modiifed radical or partial mastectomy and axillary dissection from January 2000 to December 2002. hTe patients were divided into the T1-T2 N1 and T3-T4 N1 groups. hTe effects of PMRT on the LRFFS and OS of these two patient groups were analyzed using SPSS 19.0, Pearson’s χ2-test, Kaplan-Meier method, and Cox proportional hazard model. Results: For T1-T2 N1 patients, no statistical signiifcance was observed in the effects of PMRT on LRFFS [hazard ratio (HR)=0.726; 95% conifdence interval (CI): 0.233-2.265;P=0.582] and OS (HR=0.914; 95% CI: 0.478-1.745;P=0.784) of the general patients. Extracapsular extension (ECE) and high histological grade were the risk factors for LRFFS and OS with statistical significance in multivariate analysis. Stratification analysis showed that PMRT statistically improved the clinical outcomes in high-risk patients [ECE (+), LRFFS:P=0.026, OS:P=0.007; histological grade III, LRFFS:P