Abstract: Objective： To explore the efficacy of root canal retreatment after the removal of root canal filling, and analyze the factors associated with efficacy. Methods： A total of 243 teeth from 221 patients, who underwent root canal retreatment after failure of initial root canal treatment during Jan. 2011 to Oct. 2012, were selected. According to X-ray criteria and iatrogenic factors, the 243 teeth were divided into four groups, root canal underfilling (group A), missing filling(group B), overfilling with apical radiolucent area (group C), loose filling (group D). In order to evaluate the effect of non-iatrogenic factors on root canal retreatment, the 243 teeth were divided again by age, teeth location, and root canal patency. The clinical symptom and X-ray examination was used to evaluate the efficacy. Results： Among the 243 teeth, 222 received successful root canal retreatment, and the success rate was 91.36%. The success rates were 93.45%(157/168), 91.67%(22/24), 56.25%(9/16), 97.14%(34/35)in group A, B, C, and D, respectively. According to non-iatrogenic factors, the success rates of root canal retreatment were 96.49%(165/171), 79.17%(57/72) in the cases with root canal patency and impatency, respectively, and there was significant difference between them (P< 0.05). And the success rate of patients age≥60 and < 60 years were 89.47%(136/152), 94.51%(86/91), respectively, and there was no significant difference between them. Furthermore, the success rate of front tooth and back tooth were 93.75%(105/112), 89.31%(117/131), respectively, and there was no significant difference between them. Conclusions： Root canal retreatment can obtain good curative effect. However, there is high failure rate in case of root canal overfilling. Whether root canal is patency or not is a great factor of success.