Background There is increasing evidence that serum urea nitrogen may be a risk factor for prostate cancer (PCa) and affects serum prostate-specific antigen (PSA) concentrations, but direct evidence on the association between PSA and serum urea nitrogen levels in the general population is still lacking. The purpose of this study was to demonstrate the association between serum urea nitrogen levels and PSA and PCa. Methods We conducted a cross-sectional study using the National Health and Nutrition Examination Survey (NHANES, 2003–2010) database. We performed multifactorial regression to examine the association between serum urea nitrogen levels and PSA and PCa, followed by subgroup analysis. Results This study included 5256 subjects, and after adjusting for demographic, biological and immunological variables, we observed that there was a threshold for blood urea nitrogen concentration below which each 1 ng/ml increase in serum urea nitrogen was associated with a 0.0325 ng/mL (log2 transformed) (95% CI: 0.0064, 0.0586) increase in PSA concentration, with a P trend less than 0.05 and the difference was statistically significant. Sensitivity analysis using the generalized additive model (GAM) supported a linear association between serum urea nitrogen and serum PSA concentrations when blood urea nitrogen concentrations ranged from 0ng/ml to 6.78ng/ml. Conclusion Serum urea nitrogen was independently and positively correlated with serum PSA concentration when the blood urea nitrogen concentration ranged from 0 ng/ml to 6.78 ng/ml.