To investigate the protective effect of pentoxifylline against radiation injury in patients with breast cancer. METHODS A total of 82 patients with early-stage breast cancer who underwent breast-conserving surgery and intraoperative electron radiotherapy (RT) as a boost followed by whole-breast RT in the past circa 5 years and completed the full RT dose at least 1 year before were included into this retrospective study. The patients who received prophylactic pentoxifylline (n=44) were assigned to Group A, and those who did not (n=38) to Group B. All cases were evaluated a month (early) and 1 year (late) later, scored according to the Late Effects Normal Tissue Task Force-Subjective, Objective, Management, Analytic scale and analyzed using an independent t-test. RESULTS In Group A, the score was 0,1, 2, and 3 in 24,11,seven, and two cases, respectively, in the early period and in 26,10, five, and three cases, respectively, in the late period. In Group B, the score was 0,1, 2, and 3 in 20,10, five, and three cases, respectively, in the early period, and in 15, 12, six, and five cases, respectively, in the late period. The average scores in Groups A and B were, respectively, 0.90/0.86 in the early and 0.65/1.02 in the late period. According to the t-test, there was a significant difference in the late period (p=0.001) in favor of Group A. CONCLUSION Penthoxifylline was effective in protection against the radiation injury.