Serum LacdiNAc-glycosylated prostate-specific antigen (LDN-PSA) and LDN-PSA density together with PSA and PSA density (PSAD) were measured as a diagnostic tool for prostate cancer (PCa). We included 150 patients with PCa without hormonal therapy and 41 patients without PCa obtained from the Kyoto University Hospital between 2012 and 2017. LDN-PSA levels were measured through a WFA-anti-PSA antibody sandwich immunoassay using a highly sensitive surface plasmon field-enhanced fluorescence spectroscopy (SPFS) system. Diagnostic performance of serum LDN-PSA and LDN-PSAD was evaluated by measuring the area under the receiver-operating characteristic curve (AUC). The AUCs of LDN-PSA, LDN-PSAD, and PSAD levels (0.780, 0.848, and 0.835, respectively) detected in patients with PCa were significantly higher (P= .0001, P< .0001, and P< .0001, respectively) than that of PSA (0.590). Moreover, among 143 patients with PCa who received radical prostatectomy (RP), the AUCs of LDN-PSA, LDN-PSAD, and PSAD levels (0.750, 0.812, and 0.769, respectively) detected in patients with a pathologic Gleason grade group≥ 2 were significantly higher (P= .0170, P= .0028, and P= .0003, respectively) than that of PSA (0.578). In the group comprising 35 patients who received RP with a Gleason grade group 1-graded biopsy, the LDN-PSA, LDN-PSAD, and PSAD levels were significantly different (P= .0097, P= .0024, and P= .0312, respectively). However, PSA alone could not discriminate cases with adverse features (P= .454). LDN-PSAD is a potential marker for detecting PCa and selecting candidates for RP.