Abstract: The hexagonal phasecadmium sulfide (CdS) nanomaterials as novel photoelectrode were used to construct a label-free photoelectrochemical (PEC) immunosensor for sensitive detection of prostate specific antigen (PSA) by utilizing steric hindrance effect. In the existence of target PSA, the antibody modified on the photoelectrode specifically recognizes PSA to form an immune complex, and the increase in steric hindrance on the electrode interface results in a decreased photocurrent response.The excellent photoelectric property of the photoelectrode combined with the high specificity of the immuno reaction endows the immunosensor with good analytical performance.Under optimized experimental conditions, the detection limit and the linear range for PSA were 5.0×10^-13 g/mL and 1.0×10^-12~1.0×10^-7 g/mL, respectively. Furthermore, the proposed strategy was applied for the determination of PSA content in human serum samples, the recoveries ranged from 90.0%~112.0% and the relative standard deviations (RSDs) were less than 5.0%. The results were consistent with the reference results provided by Xinyang Central Hospital.