Abstract： Objective To investigate the efficacy and safety of conversion therapy to mizoribine (MZR) for renal transplant patients who suffered MMF or Aza adverse reaction. Methods In 56 patients with adverse reactions at different time points after renal transplantation, there were 23 cases of pulmonary infection, 14 cases of bone marrow depression, 6 cases of hepatic functional lesion and 13 cases of diarrhea. The immunosuppressive protocols of these patients were changed to CNI + MZR + Pre when the adverse reaction occurred. During the follow-up period (11 to 53 months), the effect and adverse events of conversion treatment were observed. Results After conversion treatment, 1 of 23 patients with pulmonary infection was re-infected after 26 months and finally died of heart and lung function failure. In 14 patients with bone marrow depression, blood test returned to normal in 13cases. Six patients with hepatic functional lesion were administered hepatoprotection treatment and their liver function was restored without recurrence of impaired liver function. All 13 patients with diarrhea were relieved without recurrence. The serum creatinine was 123 ± 21.3 μmol/L and 119±18. 2 μmol/L before and after the conversion therapy respectively (P＞0. 05). During the follow-up period, all patients' graft function was good. The incidence of rejection was 1.7 % (1 case). Nine patients (16. 1 %) had a higher level of uric acid after conversion. One patient had finger and toe joint pain. The symptoms were relieved after symptomatic treatment. Conclusion There were high security and good effect of conversion therapy to MZR due to MMF or Aza adverse reaction. Besides, MZR conversion therapy for renal transplantation patients provided a new option for individual immunosuppression.