Abstract： Objective:To compare the diagnostic value between prostate imaging reporting and data system version 2 (PI-RADS V2) and version 2.1 (PI-RADS V2.1) for clinically significant prostate cancer (csPCa).Methods:The imaging, pathological and clinical data of 837 patients with prostatic multiparametric MRI in Second Affiliated Hospital of Soochow University from May 2015 to August 2019 were retrospectively analyzed. According to the pathological results of systematic biopsy, the prostate cancer with Gleason score (GS) ≥3+4 was csPCa. A total of 25% of the patients (209 cases) were selected using a simple random sampling, and the index lesions were scored by 2 radiologists with PI-RADS V2 and V2.1, respectively. The weighted Kappa test was used to evaluate the consistency of the scores interpreted between the 2 radiologists. The remaining cases were scored by one of the radiologists using the 2 scoring system respectively. The ROC curve was used to evaluate the diagnostic performance of the 2 scoring system for csPCa in total lesions, peripheral lesions and transitional lesions. Z test was used to investigate whether there was any difference in the detection efficiency between the 2 scoring system. Results:There were 251 patients with csPCa, including 163 patients in peripheral zone and 88 patients in transitional zone. The weighted Kappa value of total lesions, transitional lesions, peripheral lesions was 0.757, 0.653, 0.748 for PI-RADS V2 and 0.794, 0.707, 0.759 for PI-RADS V2.1, respectively. In total lesions, transitional lesions and peripheral lesions, the area under the ROC curve of csPCa detected by PI-RADS V2.1 was 0.922, 0.932, 0.854 and 0.902, 0.905, 0.817 by PI-RADS V2, respectively, and all the differences were statistically significant ( Z=4.104, P<0.001; Z=2.538, P=0.011; Z=3.350, P<0.001). Conclusion:PI-RADS V2.1 has a slightly higher consistent weighted Kappa value in evaluating prostate lesions than PI-RADS V2, and the detection efficiency of csPCa was higher than PI-RADS V2.