A new corrosion inhibitor namely N-(piperidinomethyl)-3-[(pyridylidene)amino]isatin (PPI) has been synthesized and its influence on corrosion inhibition of mild steel in IN hydrochloric acid solution has been studied by weight loss and potentiodynamic polarisation techniques. The inhibitor (PPI) showed more than 94% inhibition efficiency (IE) and an optimum concentration of 300 ppm. The inhibition efficiency of inhibitor has been found to vary with inhibitor concentration, solution temperature, immersion time and acid concentration. Various parameters (E-a, Delta G(ads), Q Delta H, Delta S) for adsorption reveal a strong interaction between inhibitor and mild steel surface. The negative Values of G(ads) indicate the spontaneous adsorption of the inhibitor on mild steel surface. Potentiodynamic polarisation studies show that PPI is a mixed type inhibitor. It inhibits mild steel corrosion by blocking the active sites of metal. Electrochemical impedance spectroscopic (EIS) techniques were also used to investigate the mechanism of corrosion inhibition. (C) 2008 Elsevier B.V. All rights reserved.