A squid by-product gelatinous protein polymer (SBP) has been extracted, characterized and examined as eco-friendly inhibitor for carbon steel in 0.5 M H2SO4 media by weight loss, electrochemical techniques. It was found that the SBP acts as a good corrosion inhibitor. The inhibition efficiency increases with increasing inhibitor concentration, but the temperature has hardly affected on the inhibition efficiency of SBP. Thermodynamic data clearly show that the adsorption mechanism of SBP on the carbon steel surface in 0.5 M H2SO4 solution is mainly physical adsorption. Moreover, the adsorption of the SBP molecules was found follows a Langmuir adsorption isotherm. Results of potentiodynamic polarization measurements revealed that the SBP acts as mixed-type inhibitor. Data obtained from EIS studies were analyzed to model inhibition process through appropriate equivalent circuit model. Theoretical parameters derived from quantum chemical calculations as well as binding energy derived from molecular dynamics simulations studies adequately corroborate the trend of experimental inhibition efficiencies of the studied inhibitors.