Objective To investigate the kinetics of PML-RARα fusion gene in acute promyelocytic leukemia(APL)to monitor minimal residual disease(MRD). Methods In induction therapy,consolidation and maintenance therapy courses, PML-RARα fusion gene was performed by RT-PCR. Results The long-term follow-up of 18 cases achieved complete remission (CR),two cases experienced molecular relapse. One case relapsed at 4 months after CR1 and achieved CR2 after induction therapy. However, molecular and hematology relapsed again at 2 months after CR2 and re-achieved CR3. The other case relapsed at 74 months after CR1 and achieved CR2 after induction treatment, who had survived for 106 months until the end of follow-up. Conclusion RT-PCR assay for detection of PML-RARα should be performed regularly during CR period so as to find molecular relapse eady. Hematological relapse could potentially be averted through treatment modification according to molecular monitoring results of PML-RARα.