To assess the distinctiveness of serum native thiol (NT), total thiol (TT) and disulfide (SS) levels in PCa patients, we created a new parameter, prostate thiol index (PTI) [tPSA (TTxPVxAge) (-1/2)]. We determined the performance of the PTI on PCa diagnosis. A total of 107 male patients (PCa:65; BPH:42) who were separated according to their Gleason scores, ISUP grades and EAU risk groups and 20 healthy subjects were included. The performances of the tests were determined. The PCa and BPH groups had lower NT and TT levels and higher SS levels than the control group. PCa patients had higher PTI, tPSA, fPSA, PSAD levels, lower fPSA%, PV and PSA-AV levels than BPH patients. TT, PTI, tPSA, fPSA, fPSA%, PSA-AV, PSAD and PV had significant diagnostic performances. PTI had the highest AUC value and accuracy, PSA-AV had the highest specificity, and fPSA had the lowest sensitivity. The performance of the PTI was the best in distinguishing PCa from BPH. PTI, tPSA and PSAD positively and PSA-AV negatively correlated with ISUP grades and EAU groups. TT can contribute to the discrimination of PCa from BPH and PTI may decrease unnecessary biopsies in clinical practice.