Background & Objective: Hypofractionation has been used in curative setting in breast conservative surgery, but still no adequate information about its application in the adjuvant setting after mastectomy in breast cancer patients. The aim of this trial was to assess the efficacy and toxicity of hypofractionation radiotherapy (40 Gy in 15 fractions) in post mastectomy breast cancer patients and to compare these results with those of post mastectomy patients treated retrospectively by conventional radiotherapy (50 Gy in 25 fractions) as regard overall survival (OS), disease free survival (DFS), locoregional disease free survival (LDFS), and toxicities. Patients & Methods: One hundred post mastectomy breast cancer patients were included into this study, they were divided into 2 groups, the 1st included 50 patients treated prospectively with hypofractionated radiotherapy regimen (40 Gy in 15 fractions), and the 2nd (control group) included 50 patients treated retrospectively with conventionally fractionated radiotherapy regimen (50 Gy in 25 fractions). Results:The 2 year overall survival were 96% & 94% respectively (p = 0.7),