Objective To quantitatively detect CA125 with self-designed synthetic gold nanoparticle probes by the colorimetric immunoassay and to initially investigate the feasibility of clinical application .Methods The capture antibody of detective CA125 was conjugated to the gold nanoparticle surface for preparing the gold nanoparticle probes .The gold nanoparticle aggregation was formed by the antigen-antibody immunoreaction .CA125 was quantitatively detected by the colorimetric immunoassay .Results The gold nanoparticle probes was successfully prepared ,which could detect the serum CA125 content rapidly and conveniently ,the de-tection results were coincident with the pathological diagnosis .The lowest limit of quantitation was 0 .5 U/mL ,which was far lower than that in ELISA .Conclusion This gold nanoparticle probes are simple to be prepared ,rapid and easy to operate with low cost , and have the important application value in clinical early detection of ovarian cancer marker CA 125 ,especially in the primary hospi-tals .