Purpose:To evaluate the efficacy of 5αRIs for BPH patients with large prostate (>80ml) at 3 years follow-up after TURP prospectively.Materials and methods:Eight-seven patients with large BPH were recruited by three clinical centers from January 2007 to October 2014 in the study.Patients were randomized into a trial group (n=45) and a control group (n=42).The trial group took 5αRIs (either finasteride or dutasteride) after TURP, which lasted 3 years, while the control group took placebo.We evaluated the baseline characteristics and the indicators before, peri and after TURP(including PV, PSA,Qm,PdetQm,IPSS,QoL,PVR,AUR,HU,UTI,OM,RR,CDAO,HDAO,Re-TURP).Results:There were no significant differences in the baseline characteristics and the indicators between the trial group and control group before and peri TURP.In 6 months after TURP, there were significant differences in PSA and HU between the trial group and control group.But there were no significant differences in other indicators.And in the trial group, there were no significant differences in all indicators between the finasteride group and dutasteride group.In 3 years after TURP,there were significant differences in PV, PSA,Qm and HU between the trial group and control group.And in the trial group, there were significant differences in the PV, PSA,IPSS and QoL between the finasteride group and dutasteride group, but there were no significant differences in Qm,PdetQm,PVR,HU,UTI and Re-TURP between them.Conclusions:After TURP of large BPH, taking 5αtRIs for 3 years can improve PV, PSA,Qm and HU, and dutasteride is better than finasteride in the improvement of PV, PSA,IPSS and QoL.