Corrosion is the process of metal oxidation in the presence of oxygen which causes losses in the industrial field. This study was conducted with the aim to determine the effectivity of water-soluble chitosan from crab shells as a corrosion inhibitor on iron in 1M HCl media. Crab shell waste was demineralized and deproteinated to obtain chitin. Chitin obtained was then deacetylated to obtain Water Soluble Chitosan (WSC). The inhibition efficiency of WSC on iron corrosion in HCL 1 M media was determined by the weight loss method. The results showed that the corrosion rate decreased with the increase of inhibitor concentrations of 0, 100, 300 and 500 ppm. However, the increase in temperatures (303, 313 and 323 K) also increased the corrosion rate. The inhibition efficiency increased as the inhibitor concentration increased. The optimum efficiency occurred at a temperature of 303 K and a concentration of 500 ppm which was equal to 98.94%. The corrosion rate decreased with the increase of pH values (3, 4 and 5). WSC adsorption from crab shell waste on the surface of iron in 1M HCl media follows the isothermal model of Freundlich adsorption. In the thermodynamic study, the values of Ea, ΔH ΔS, and ΔG0 Ads were used to determine the adsorption of iron inhibitors. The results of the study showed that the reaction is a physical reaction (physisorption), endothermic, and spontaneous.