Natural products of plant origin are used as green corrosion inhibitors, because plant extracts are ecologically acceptable, nontoxic, environmentally friendly, readily available and renewable sources of materials. The corrosion inhibition efficiency of peel of Cucurbita maxima (PCM) on mild steel in 1N H₂SO₄ was studied using weight loss measurement and Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The inhibition efficiency value reaches 95% at 3% v/v concentration of PCM. Totally ten active constituents in plant extract were identified by GC-MS analysis. Adsorption, kinetic and thermodynamics properties of the plant extract also discussed.