The environmental friendly inhibitor system L-cysteine-Zn 2+ has been investigated by weight loss method. A synergistic effect exists between L-cysteine and Zn 2+ system. The formulation consisting of 250 ppm of L-cysteine and 50 ppm of Zn 2+ offers an excellent inhibition efficiency of 99%. Polarization study reveals that this formulation functions as anodic inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra study leads to the conclusion that the Fe 2+ -L-cysteine complex formed on the anodic sites of the metal surface controlled the anodic reaction, and Zn(OH)2 formed on the cathodic sites of the metal surface controlled the cathodic reaction. A suitable mechanism of corrosion inhibition is proposed based on the results obtained from weight loss study and surface analysis technique. Synergism parameters have been calculated. They are found to be greater than 1, suggesting that a synergistic effect exists between L-cysteine and Zn 2+ .