The inhibition effect of tryptophan on the corrosion of LY12 aluminium alloy in 1M HCl solution,20 %(wt.%) CaCl2 solution and 3.5%(wt.%) NaCl solution were investigated through polarization techniques,electrochemical impedance spectroscopy (EIS) and weight loss method,meanwhile SEM was used to observe the corrosion morphology of aluminium alloy.The results revealed that LY12 was corroded in these three corrosion mediums to some extent and tryptophan could significantly inhibit the corrosion of aluminium alloy.The inhibition efficiency (η) increased with the increasing concentration of tryptophan,and the best inhibition efficiency was about 87% in 1M HCl solution with the concentration of 0.008M tryptophan.The addition of tryptophan influenced the hydrogen evolution reaction which was the main electrode reaction in 1M HCl solution,hence then tryptophan was a cathodic corrosion inhibitor.While in 20 % CaCl2 and 3.5% NaCl solutions tryptophan was adsorbed to anodic areas which increased activation energy of interface reaction as an anodic corrosion inhibitor.