The inhibition efficiency (IE) of the hydrochloride salt of chitosan biguanidine (CBG-HCl, a green organic compound) on stainless steel alloy (SS) corrosion in 0.5 M H2SO4 solution was documented in this work. Data reported for electrochemical impedance spectroscopy (EIS) and potentiodynamic analysis confirmed increasing of the corrosion resistance of stainless steel in 0.5 M H2SO4 solution in the presence of CBG-HCl with a synergistic effect of KI. Potentiodynamic experiments also indicate that the blend of CBG-HCl-KI works as a mixed-type inhibitor for stainless steel alloy corrosion. The best information gathered agreed with the Langmuir isotherm model. The corresponding normal Gibbs inhibitor adsorption free energy implied that the processes are random and involved two forms of interactions, chemisorption and physisorption. The highest inhibition efficiency (88 %) in this work was reported for 400 ppm of CBG-HCl blended with 800 ppm KI. In fact, with a long immersion time, the efficiency of CBG-HCl inhibition remains effectively high, demonstrating its good stability in the 0.5 M H2SO4 medium.