Objective To evaluate the value of semi-quantitative indices of 68Ga-prostate specific membrane antigen (PSMA)-11 PET/CT in differentiating malignant and benign prostate lesions.Methods From November 2017 to June 2018,30 patients (age:52-86 years) who underwent 68Ga-PSMA-11 PET/CT imaging in the Third Affiliated Hospital of Sun Yat-sen University were retrospectively analyzed,and the serum total prostate specific antigen (tPSA) and free prostate specific antigen (fPSA) were examined within 1 week before PET/CT imaging.Semi-quantitative indices of 68Ga-PSMA-11 PET/CT on prostate lesions were measured by automatic segmentation algorithm method,including PSMA-related lesion volume (VPSMA),maximum standardized uptake value (SUVmax),mean standardized uptake value (SUVmean),peak standardized uptake value (SUVpeak) and total lesion uptake value of PSMA (TLUPSMA).The indices were compared between malignant and benign prostate lesions,and the optimal cut-off values for differentiating malignant and benign prostate lesions were obtained by receiver operating characteristic (ROC) curve analysis.Results According to the pathological results,19 patients had malignant lesions and 11 were with benign diseases.The differences of tPSA,SUVmax,SUVmean SUVpeak and TLUPSMA between malignant and benign prostate lesions were statistically significant (u values:17.00-48.00,all P＜0.05),but there were no significant differences of fPSA,fPSA/tPSA and VPSMA between 2 groups (u values:64.00-99.00,all P＞0.05).The optimal cut-off value of tPSA was 18.30 μg/L for differentiating malignant and benign prostate lesions,with sensitivity of 13/17 (PSA of 2 patients were missing),specificity of 9/11 and area under curve (AUC) of 0.743.The optimal cut-off values of SUVmax,SUVmean and SUVpeak were 5.50,3.09 and 3.56,respectively,with all corresponding sensitivity of 18/19,all specificity of 9/11,and AUC of 0.902,0.907 and 0.919,respectively.The optimal cut-off value of TLUPSMA was 54.81 cm3,with sensitivity of 14/19,specificity of 9/11 and AUC of 0.804.Conclusion The semi-quantitative indices of 68Ga-PSMA-11 PET/CT are valuable for differentiating malignant and benign prostate lesions,in which SUVpeak is superior to other indices.