Corrosion is one of the problems that is often found in daily life especially in petroleum and gas industry. Carboxymethyl chitosan- (CMC-) benzaldehyde was synthesized as corrosion inhibitor for steel.Corrosion rate was determined by potentiostatic polarization method in HCl 1 M. Dripping and coating, two different treatment, were used to drop and coat steel by CMC-benzaldehyde. The results showed that CMC-benzaldehyde could inhibit the corrosion rate of steel with concentration of 1 g, 3 g, 5 g, and 7 g in 60mL of solvent. Coating steel with CMC-benzaldehyde with concentration of 7 g/60mL of solvent and starch of 0.1 g/mL showed the highest efficiency to inhibit corrosion rate of steel. These treatments give corrosion efficiency of 99.8%.