Abstract: Assembling of L-cysteine on gold electrode was described.Electrochemical behavior of p-aminophenol at L-cysteine modified gold electrode was studied by cyclic voltammetry.It was found that in a phosphate medium of pH 6.54,and using the scanning rate of 100 mV·s-1,better reversibility of the electrode reaction of p-aminophenol at the L-cysteine modified gold electrode was obtained as compared with the bare gold electrode,and that significant electrocatalytic activity of the modified electrode toward the reaction of p-aminophenol was observed.Condition of this electrochemical reaction was optimized and the method was applied to the determination of p-aminophenol in drinking water by measuring the oxidative peak current with the linear scanning method.A brief discussion on the mechanism of the electrocatalysis was given.