The inhibition efficiency of crab shell (CS) extract was investigated on mild steel (MS) in 1M H2SO4. The corrosion-resistant behavior was assessed by weight-loss method, thermodynamic and polarization studies. The maximum inhibition efficiency of 93.20% was recorded at 12 hours of immersion time at optimum concentration. The inhibition efficiency diminishes with increasing temperature. The results of the Langmuir adsorption study support the nature of monolayer adsorption. The activation and thermodynamic analysis demonstrated that the reaction is natural and spontaneous. The mixed type character of the inhibitor was shown by potentiodynamic polarization studies. The values of Rct and Cdl obtained from EIS indicated that the CS extract acts as an effective inhibitor. SEM examination revealed the creation of the protective layer on the surface of the mild steel.