The inhibitive effects of the natural polymer namely, carboxy methyl chitosan (CMCH) and carboxy
methyl Cellulose (CMC) for the corrosion of aluminum in 0.5 M HCl solution was investigated using weight loss
measurements, galvanostatic, and potentiodynamic anodic polarization techniques. The results drawn from these
techniques indicated that the inhibition efficiency increased with the concentration of inhibitor but decreased with
temperature. Some activated thermodynamic parameters were computed. The inhibition efficiency of the CMCH is
more than CMC depends on the chemical structure of the inhibitor.. Inhibition was explained in term of the
adsorption of these compounds on the aluminum surface. The adsorption process is fitting a Temkin adsorption
isotherm. Polarization data proves that these inhibitors are mixed inhibitors. It was found that CMCH and CMC
compounds protect the aluminum surface from pitting attack in chloride containing solution by shifting the pitting
corrosion potential to more noble direction.