The inhibition of corrosion of mild steel in 1M HCl and H2SO4 acid solutions by Ervatamia coronaria has been evaluated by a weight loss method. The results indicate that the plant extract possesses a significant anticorrosion effect. Ervatinine, the alkaloid present in the leaves of the plant has been isolated and its anti-corrosive potential has been investigated using weight loss, electrochemical impedance, Tafel polarization, scanning electron microscope and X-ray diffraction techniques. The results suggest that ervatinine acts as a good corrosion inhibitor. The adsorption of ervatinine on mild steel surface obeyed Langmuir adsorption isotherm following physisorption mode. The thermodynamic parameters such as adsorption equilibrium constant, standard free energy of adsorption and activation energy have been calculated to determine the mechanism of corrosion inhibition. Results of electrochemical measurements such as potentiodynamic polarization and electrochemical impedance spectroscopy revealed the mode of inhibitive action and adsorption of inhibitor molecules. Further, surface morphological examination supports the protective film formation by ervatinine on mild steel surface. The results confirmed the influencing role of ervatinine in the inhibition of corrosion of mild steel in acid media by extract of E. coronaria.