Inhibition effect of (2E)-2-(3-hydroxy-2-methoxybenzylidene) hydrazinecarbothioamide (HMBHC) on the corrosion of mild steel in 0.5 M HCl solution has been investigated using potentiostatic polarization and electrochemical impedance spectroscopic techniques. The inhibition efficiency increases with increase in inhibitor concentration and with increase in temperature. The polarization study show that the HMBHC acted as mixed type of inhibitor. The kinetic and thermodynamic parameters have been calculated and discussed in detail. The adsorption of inhibitor on the metal surface is found to be through chemisorption and followed Langmuir' s adsorption isotherm. The surface morphology of the specimen has been studied by scanning electron microscopy study.