Background: After the mastectomy, the complication is different depending on the sequence and method of breast reconstruction and Radiotherapy (RT). The aim of the current study was to investigate complication rates, related factors, and time to complications in breast cancer patients who underwent mastectomy with immediate autologous breast reconstruction (IABR) and adjuvant RT. Materials and Methods: Between April 2009 and January 2017, 52 patients underwent mastectomy with IABR followed by RT. Medical records of patients were retrospectively reviewed. Complications occurring after RT initiation were evaluated in four aspects: fat necrosis, wound infection, revision surgery, and re-reconstruction and classified into: 1) minor complication requiring only conservative treatment, and 2) major complication requiring surgical correction. All patients received RT on the chest wall including total flap. Ipsilateral axillary, supraclavicular and internal mammary regions were included at physician’s discretion. Median RT dose was 50.4 Gy (range, 50.4 – 59.4 Gy). Results: Median follow up duration was 22.3 months (range, 5.3-98.6 months). Complication after RT initiation occurred in 9 (17.3%) patients. Six (11.5%) patients showed minor complications. Three (5.8%) patients developed major complications. Median time to occurrence of complication after RT was 8.6 months (range, 1.8–25.1 months). Two-thirds of complications occurred within one year, while 88.9% occurred within two years after RT. No factor showed correlation with complication. Conclusions: IABR followed by adjuvant RT may be a reasonable option for patients who underwent mastectomy, in terms of postoperative complication. Complications occur most frequently within 1 year after initiation of RT, and most occur within 2 years.