Binary thiolates self-assembled monolayers (SAMs) on gold have been prepared efficiently by using an electrochemical oxidation combining with replacement reaction method. The electrochemical results show that both the SAMs of mercaptoacetic acid (MAA) and 1-dodecanethiol (DT) on gold surface are oxidized at certain anodic potentials (noting: it is not oxidative redeposition of alkanethiolate monolayers on gold surface), and the degree of electrochemical oxidation of single thiolates-SAMs is function of the polarization potential and polarization time. Therefore, formation of binary MAA-DT thiolates-SAMs can be achieved if MAA or DT is present in solution after the electrochemical oxidation of DT or MAA SAMs on gold electrode. In this case, the ratio of MAA to DT on the binary thiolates-SAMs can be easily controlled by controlling polarization potential and/or polarization time. The present approach enables us to prepare homogeneously binary SAMs with different composition, and assess the electrochemical oxidation stability of single thiolates-SAMs by means of cyclic voltammetry measurements of redox probe.