A mercaptobutamine combined Cu（II） absorbing Au colloid/PSA antibody biosensor for the determination of PSA in serum is reported.The modified electrode is simply self-assembly prepared.In PBS buffer solution of pH 5.2

differential-pulse voltammetry（DPV） is used for measurement.The peak currents of catholic DPV peaks decrease with the addition of PSA into the buffer solution while the peak potentials remain the same.The decreasing value of peak current is linear with PSA concentration in the range of 0.005-0.48 mg/L.The detection limit is 2 μg/L.And the relative standard deviation for 40 μg/L PSA is 2.9 %（n=8）.The stability of this electrode is satisfactory without serious interference.The method is successfully employed to determine PSA antigen in serum samples.