The inhibition efficiency of an acid extract of Antigonon Leptopus (AL) used as corrosion inhibitor for mild steel in 1 M HCl medium is inspected by weight loss, temperature and electrochemical studies in the presence and absence of extract. The polarization studies reveal that this AL extract as a good mixed type inhibitor. Thermodynamic parameter such as free energy value was negative, that indicates spontaneous adsorption of inhihibitor on mild steel (MS). The Antigonon Leptopus extract obeys Langmauir and Temkin adsorption isotherm. FTIR spectra revealed that the protective film formed between the active principle of the AL extract and Fe2+. All the reported Antigonon Leptopus extract was found to inhibit the corrosion of mild steel in HCl acid media.