The inhibition effect of Carboxymethylchitosan (CMCT), Cu2+, and CMCT + Cu2+ mixture on the corrosion of mild steel in 1 M HCl has been investigated using gravimetric and electrochemical techniques. CMCT+Cu2+ mixture acts much more effectively than the inhibiting action of each additive separately. In addition, higher efficiency is achieved for the mixture of 20 mg L-1 CMCT + 10(-4) M CU2+. The efficiency of the optimal mixture increases with the temperature in the range 298-353 K. Activation energy of corrosion reaction in the presence of the optimal mixture of the inhibitors is much lower than that exhibited in 1 M HCl solution. The inhibition mechanism proposed in this paper is based on the results of conductometric investigations. (C) 2007 Elsevier Ltd. All rights reserved.