TThe effect of isatin on the corrosion of Cu-20%Zn-2%Al (alloy I) and Cu-31% Zn (alloy II) in NaCl solution has been studied using different electrochemical techniques [open circuit, potentiodynamic, and impedance spectroscopy (EIS)]. The two copper alloys were used in condenser tubes of heat exchanger for power station plant in Egyptian financial and industrial company Assiut factories. The steady state potential Es.s values increase to more negative values by increasing NaCl concentration which indicated that the destruction of pre-immersion passive film formed on the Cu-Zn surfaces. The corrosion rate of the two alloys decreased by increasing concentration of isatin, which indicated the effect of isatin as a corrosion inhibitor. The inhibition efficiency of isatin in 0.1M NaCl solution was 88.5 % in alloy I and 73.9 % in alloy II at a concentration 0.01M of isatin. The significant inhibition processes due to the adsorption characteristics of isatin on the two alloys surface. The chemical composition of alloy I was more resist to corrosion in NaCl solution than the chemical composition alloy II due to presence of Al.