Objective：To evaluate the effectiveness of flexible ureteroscopy（F-URS） and laser lithotripsy in the treatment of infectious renal calculi with multi-drug resistant bacteria infection. Methods：The clinical data of 15 patients who were diagnosed as infectious renal calculi with multi-drug resistant bacteria infection and treated by flexible ureteroscopic lithotripsy in our department between 2016 January and 2017 December were retrospectively reviewed. In all patients，ureter stent was placed for 2 weeks before surgery and 2 to 4 week after surgery，preoperative intravenous sensitive antibiotics was used for at least 1 week. One stage or multi-stage surgery was processed in different cases. Patient demographics（age，sex，body mass index），stone characteristics（stone size，location） and pe－rioperative measures（duration of operation，hospitalization and stone free rate（SFR） and complication rates） were reviewed. Results：A total of 15 patients were included in the study and successfully treated by F-URL. The mean stone size was （2.07±0.72） cm. The mean duration of operation was （52.87±18.97） min. The mean length of hospital stay was （3.40±2.06） d. Renal pus substance was observed in 8 patients. Five patients underwent second stage surgery and 2 patients underwent third stage surgery. One stage SFR and the total SFR was 53.3%（8/15） and 80.0%（12/15），respectively. Residual fragments were failed to be cleaned in 3 patients（20.0%） due to inability to reach in result of location in an isolated or enclosed lower calyx. Postoperative complications were ob－served in 4 patients[26.7%；fever（n=2），persistent hematuria（n=1），mild ureter injury（n=1）]. No severe complications or mortality occurred. Conclusion：In spite of challenge in skill and risk of severe complication in treating infectious renal calculi with multi-drug resistant bacteria infection，F-URS can be a safe and effective modality in premise of fully preparation，duration reduction，skilled and staging operation.
