Abstract: Balb/c mice were immunized with carbohydrate antigen 125 (CA125), and a competing sandwich immunoassay was used to screen positive clone of hybridoma cell, finally one monoclonal antibody against CA125 was got successfully. Applications of the antibody in immunoradiometric assay (IRMA) and chemiluminescence immunoassay (CLIA) show it is an ideal substitute of coating part in the sandwich system. We performed a normal range studies in which all healthy women had assay values less than 35 U/mL. A direct relationship exits between ELIA and IRMA with commercial kits, correlative equations are y=0.85x+11.1(r＝0.932) in CLIA, y=0.87x－12.8(r＝0.983) in IRMA, respectively. New antibody is stable at 37 ℃ for 2 weeks.