Owing to the unique structure and functionality of ultrathin precious metal film, it is of great significance to innovate the preparation method and expand the electrochemical applications of ultrathin precious metal film. Herein, by using an ultrathin film of a less electron-conducting electrodeposited Se as the template and a subsequent galvanic replacement reaction (GRR) with HAuCl 4 , the ultrathin Au film modified Pd-electroplated glassy carbon electrode (Au Se /Pd/GCE) was fabricated. The electrocatalytic and electroanalytical performance of the modified electrode was studied. The electrocatalysis performance of the Au Se /Pd/GCE toward oxidation of ethanol was investigated in alkaline solution via cyclic voltammetry, and then the ethanol amperometric sensor was constructed. Compared with the bare Pd electrode, the AuSe/Pd/GCE showed the higher electrocatalytic active toward the electrocatalytic oxidation of ethanol. Under the optimal conditions, the Au Se /Pd/GCE showed a linear amperometric response to ethanol concentration from 0.025 mmol/L to 10.000 mmol/L with a sensitivity of 0.94 (mA·cm -2 )/(mmol·L -1 ), being superior to most of relevant reports. The new method for preparing the ultrathin precious metal film by GRR with the uniform electrodeposited ultrathin film of a less electron-conducting material presented here was expected to be widely used in the preparation of nano-electrocatalysts for their electrocatalysis and electroanalysis applications.