The inhibition effect of Ni2+ cation, 3-methyl pyrazolone (3-MP) and mixture of them on the corrosion of carbon steel in 0.5 M H2SO4 solution was studied using weight loss, galvanostatic and potentiodynamic anodic polarization techniques The inhibition efficiency increases with increasing concentration of Ni2+ and 3-MP. The mixtures of Ni2+ and 3-MP improved the inhibition efficiency The formation of complex Compound was discussed depending on the results derived from UV-visible spectrophotometric measurements as well as conductometric titration (c) 2009 Elsevier B.V. All rights reserved