The recent trend of utilizing plant extract and pharmaceutical material as a corrosion inhibitor in the acidic medium has been increased. The isolation of vasicine from the extract of plant Adhatoda vasica (AD) shows a good inhibitive performance on mild steel material in 1N HCl. The isolation of vasicine compound was confirmed by characterization of C13NMR, and LC- MS. Vasicine inhibition effect on mild steel corrosion and its mechanism by weight loss method, polarisation technique and electrochmical impedance method was carried out . Weight loss method indicated the inhibition efficiency of vasicine on corrosion of mild steel in 1N HCl solution increases with increase in concentration and decreases with rise in temperature. Polarization measurement show that a vasicine acts as mixed type inhibitor. The AC impedance study reveals that the charge-transfer process controls the corrosion of mild steel. The increase in activation energies of corrosion process in the presence of the vasicine retarded the rate of corrosion of mild steel in 1 N HCl solution. The protective film formed over the surface was confirmed by SEM Analysis. The vasicine compound reduces the permeation current. The nature of adsorption of the extract on mild steel surface follows Langmuir isotherm. The result of AC Impedance was correlating with the result of polarization measurement and Scanning electron microscopy (SEM)