The effect of Cl -and Br -anions as aggressive species to breakdown the passivity of Ni electrode in H 2 SO 4 solution was studied using galvanostatic polarization technique. Low concentrations of these anions lower than 1×10 -4 M have no effect on the passivity of nickel, while high concentrations of these anions destroy the passivity and initiate the pitting potential before the oxygen evolution region. Raising the solution temperature shifts the breakdown potential towards the more negative direction. This could be attributed to the more destruction of the passivity by halides anions with increasing temperature. The addition of some synthetic pyridinone derivatives to the aggressive chloride solutions shifts the pitting potential to more positive values indicating the resistance to pitting attack in chloride containing solution.