The inhibition effect of Phyllostachys nigra Munro leaves’ extract (PMLE) on cold rolled steel (CRS) and zinc in 0.2 M citric acid (H3C6H5O7) solution was studied by weight loss, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) methods. Quantum chemical calculation of OFT including the solvent effect was applied to investigate the adsorption mode through light on chemical molecular structure. The results show that PMLE is a good inhibitor for both steel and zinc in 0.2 M H3C6H5O7 solution, and inhibition efficiency follows the order: zinc > steel. The adsorption of PMLE on both metal surface obeys Langmuir adsorption isotherm. (C) 2014 Elsevier Ltd. All rights reserved.