The corrosion of aluminum and aluminum-copper alloy in 0.1 N NaCl solution has been studied by linear polarization technique. Current-potential data were obtained from Which I(corr) values and corrosion rates were estimated using Stern-Geary equation and Faraday's laws. The phosphatizing chemical, thermoil granodine (trade name) was used as the inhibitor to study the effect of inhibitor on the corrosion of Al and 4 % Cu - Al alloy in chloride solutions. The optimum inhibitor concentration for maximum inhibition was determined and the effectiveness of the inhibitor was evaluated. The inhibition efficiency ranged from 40 to 65% for pure aluminum and 70 to 96% for aluminum-copper alloy.