Abstract: Objective To explore the curative effect and irradiated volume of organs at risk （OAR） of two radiotherapy（RT） techniques for breast cancer patients after conservative surgery. Methods From June 2012 to December 2012，70 early breast cancer patients were enrolled in this study with 35 patients in the simultaneous integrated boost intensity modulated radiotherapy （SIB） group and other 35 patients in the conventional radiotherapy （CRT） group. The toxicity effects，including acute and late skin reaction，bone marrow suppression， pharyngeal and digestive tract reaction were observed. The cosmetic effect， treatment time and local control of tumor were compared between both groups. Meanwhile， the three dimensional treatment planning system was used to compare the irradiated volume of OAR under SIB and CRT plan. Results The incidences of acute and chronic skin reactions were higher in SIB group versus CRT group（P＜0.05）. The cosmetic satisfactory rate of SIB group was 82.9％ （29／35）， similar with the 77.1％ （27／35） of CRT group （P＞0.05）. The duration of hospitalization of SIB group was （39.74±1.55） d， shorter than （45.60±2.35） d of CRT group with significant difference （P＜0.05）. Compared with CRT group，there were lower pulmonary V20 in SIB group（P＜0.05）. Until the follow-up date，all patients were survival. There was no significant difference in the local control rate between both groups. ConclusionIn the early breast cancer after breast conserving surgery， SIB has considerable cosmetic effect and local control rate as CRT. SIB shortened the treatment time， reduced the volume of lung irradiated at 20 Gy，and can be used in patients with breast cancer after breast conserving surgery.