Previous studies have suggested that there is a positive correlation between prostate‐specific antigen (PSA) levels and prostate volume (PV). A better understanding of the possible influence of PV on a ratio of free to total PSA (f/tPSA) may improve the diagnostic value of the prostate disease. The study group consisted of 342 men with lower urinary tract symptoms (LUTS). All patients underwent urinary tract ultrasonography and had tests carried out on PSA, serum glucose, total cholesterol, triglyceride, HDL, LDL and blood pressure. Univariate and multivariate analyses were used to assess the associations between prostate volume and f/tPSA value. We found no obvious relationship between prostate volume and f/tPSA value when PSA >10 ng/ml but did observe a positive correlation when 4 ng/ml < PSA ＜ 10 ng/ml (hazard ratio HR: 0.0012; 95% confidence interval CI: 0.0009–0.0248). With increasing prostate volume, multivariate analysis showed an obvious increase in f/tPSA value (HR: 0.0011; 95% CI: 0.0007–0.0015) (p ≤ .0001). We confirmed that prostate volume could affect the f/tPSA levels in serum. There was an obvious positive correlation between prostate volume and f/tPSA level when PSA levels were between 4 and 10ng/dl. There was no significant correlation between prostate volume and f/tPSA value when PSA >10 ng/ml.