To investgate the effect of properative transitional zone index (TZI) on the outcome of transurethral resection of prostate (TURP). A retrospective analysis was performed on 206 patients with TURP who were admitted to our hospital from January 2016 to September 2018. All patients underwent transrectal ultrasound (TRUS) to determine the total prostate volume (TPV) and the transition zone volume (TZV). Patients were divided into two groups according to TZI (TZV/TPV) (group A: TZI<0.5, group B: TZI≥0.5). We collected data 6-months after surgery including international prostate symptom score (IPSS), quality of life score (QOL), maximum flow rate (Qmax), and postvoiding residue (PVR) to compare the difference of the postoperative outcome of two groups, while the IPSS was subdivided into voiding (IPSS-v) and storage(IPSS-s) symptoms, and the changes of IPSS, IPSS-v, IPSS-s, QOL, Qmax and PVR before and after surgery were analyzed. The treatment efficacy was determined as the changes of IPSS (post/preoperative IPSS: %IPSS), QOL (preoperative QOL-postoperative QOL: ΔQOL) and Qmax(preoperative Qmax-postoperative Qmax: ΔQmax). Pearson linear correlation analysis was employed to estimate the correlation of TZI and %IPSS, ΔQOL and ΔQmax, respectively. A total of 126 patients were in Group A, and 80 patients were in group B. 1. The preoperative clinical data of the two groups were compared. There were no significant differences regarding age, IPSS, IPSS-v, IPSS-s, QOL, Qmax, and PVR between two groups (all 0.05). However, the TPV of patients in group B (74.57±29.25) ml was significantly larger than that in group A (46.25±24.56) ml, 0.001. While the postoperative follow-up outcomes of the two groups were compared, we found that IPSS-s (0.079), QOL (0.710), and PVR (0.651) were not statistically different between the two groups, but the postoperative IPSS, IPSS-v, and Qmax (8.50±5.75 vs 6.38±4.36, 4.03±3.75 vs 2.63±2.5, and (16.54±4.43) ml/s vs (18.94±4.84) ml/s, all 0.05) were significantly different between the two groups. 2. Postoperative IPSS, IPSS-v, IPSS-s, QOL, Qmax and PVR were significantly different from those before surgery in two groups, respectively. 3. Pearson linear correlation analysis showed a significant positive correlation between TZI and ΔQmax (0.32, 0.01), a weaker negative correlation between TZI and %IPSS (-0.22, 0.01), and no correlation between TZI and ΔQOL (0.08, 0.238). There may be a correlation between the outcome of TURP and TZI, and the outcome of TURP may be better in patients with TZI ≥ 0.5.