Abstract: An electrochemical sensor of captopril (CPT) modified,selfassembled Au-electrode was prepared,and the formation of mono-molecular membrane on the surface of Au-electrode was characterized.As shown by the results of the study of electrochemical behavior of coenzyme Q (CZM Q) at the CPT modified electrode,the electrode reaction was an one electrontransferring quasi-reversible reaction,and linear response in the concentration range of 5.0×10-6-6.0×10-5mol·L-1 of CZM Q was obtaioned,with a detection limit of 2.0×10-6mol·L-1.The constant of rate of heterogeneous electron-transfer (ks) was determined and its value calculated by the Nicholson method was 5.4×10-3cm·s-1,and the mechanism of factors affecting the value of ks of electrode reaction of CZM Q at the electrode was discussed.Conditions affecting the stability of the CPT modified electrode was also examined.