The inhibition effects of 8-hydroxy quinoline (HQ) and 3-formyl 8-hydroxy quinoline (FQ) on corrosion of mild steel in hydrochloric acid was investigated. It was studied through weight loss, polarization and electrochemical impedance spectroscopic techniques. The results indicated that the corrosion inhibition efficiency and extent of surface coverage were increased with increase in inhibitor concentration and decreased with increase in temperature and acid concentration. The thermodynamic parameters were evaluated for corrosion inhibition process. The inhibitors follow Langmuir adsorption isotherm. The compound FQ showed more corrosion inhibition efficiency than HQ. (c) 2007 Elsevier B.V. All rights reserved.