Due to high sensitivity and good selectivity, electrochemical immunosensor is often used to detect tumor markers. Prostate-specific antigen (PSA) is the most validated tumor marker for prostate cancer. In this work, mesoporous silica nanoparticles (MSNs) were used to increase the fixation capacity of primary antibody, and silver nanoparticles (Ag NPs) were used to enhance the electron transfer rates. Silver hybridized mesoporous silica nanoparticles (Ag@MSNs) were synthesized and used as electrode material. Hydroquinone (HQ) generated a stable electrochemical signal and was used as a mediator. Based on the specific antibody-antigen interaction, a label-free immunosensor was developed for the sensing of PSA. The current method allows us to detect PSA over a wide concentration range from 0.05 to 50.0 ng ml(-1) with a detection limit of 15 pg ml(-1). The proposed immunosensor was used to determine PSA in human serum with satisfactory results.