The therapeutic value of postoperative radiotherapy (RT) for squamous cell cancer of the breast (SCCB) is unclear. This retrospective study used a population-based national registry to determine the impact of postoperative RT on survival of women with SCCB. The Surveillance Epidemiology and End Results (SEER) database was used to identify females with SCCB who underwent primary surgical resection from 1973 to 2012. Kaplan-Meier survival analysis and Cox regression proportional hazard methods were used to determine the impact of RT following resection associated with cause-specific survival (CSS) and overall survival (OS). A total of 523 patients met the eligibility criteria. The median follow-up time was 55 months, the 10-year CSS and OS rates were 65.6%, and 46.0%, respectively. A total of 167 patients (31.9%) received postoperative RT. Multivariate analysis indicated that advanced pT and pN stage, and no postoperative RT were independently associated with poor OS; advanced pT and pN stage were independently associated with poor CSS. Postoperative RT was significantly associated with improved 10-year OS (54.5% vs. 42.0%, P =.001), but had no effect on CSS (P =.217). Analysis of patients with different stages of SCCB indicated that RT was associated with improved CSS (P =.047) and OS (P <.001) in those with stage II cancer and improved OS in patients with stage pN0 cancer (P <.001). Postoperative RT improved the survival of SCCB patients, especially in those with stage II and stage pN0 cancer.