In this study, we demonstrated that an amplitude-sensitive paired surface plasma wave biosensor (PSPWB) is capable of real-time detection of prostate-specific antigen (PSA) in diluted human serum without labeling. Experimentally, the detection limit of PSPWB was 8.4 × 10-9 refractive index unit (RIU) and the PSPWB could measure PSA in a phosphate buffered saline solution from 10 fg/mL (∼300 aM) to 100 pg/mL (∼3 pM) successfully, with demonstration of a linear relationship between PSA concentrations and surface plasmon resonance (SPR) signals. Therefore, results were obtained over a wide dynamic range 5 orders of magnitude for analyte concentration. In addition, the PSPWB successfully detected PSA in diluted human serum as well. These experimental results indicate that the PSPWB is capable of detection with high sensitivity over a wide range by using SPR-based biosensors and has a capability of detecting biological analytes in clinical sample without complicated operating procedures.