Psa assay method and reagent

The present invention provides a simple and high-precision species measuring method step reaction by PSA, where no carrier is used having different average particle sizes. Also it provides a reagent for the same. The PSA assay method comprising: using two types recognize different epitopes of anti-PSA monoclonal antibody-immobilized insoluble carrier, the carrier has the same but larger than the average particle size of 0.20μm or less to 0.40μm, said two type of anti-PSA monoclonal antibodies were reacted with both free PSA and PSA-ACT anti-PSA monoclonal antibody, the PSA and PSA-ACT is α1- antichymotrypsin complex; and reacting the carrier contacting the sample with the presence of agglutination accelerator.