The electrochemical passivation behavior of Ni in H2SO4 solutions was studied by the galvanostatic anodic polarization method. The data of the polarization curves relied on the polarizing current, Iimposed, acid concentration, C, and the temperature, T. The polarized curve elucidated various characteristic regions confirming various oxidation processes. The 1st region is recognized by a rapid jump in the Ni electrode potential E (zone I), due to the decay of H2 over-voltage. A large discrete 1st potential arrest, a, coincides with the formation of Ni+ ions, while the 2nd potential arrest, b, matches the electro-oxidation of Ni+ ions to Ni2+ ions. The second increase in the potential, E (zone II), harmonizes the onset of passivity due to the countenance of Ni2O3. The duration time, τ, of the two arrests a and b decrease with increasing the Iimposed, T, and the acid concentration, C. The thermodynamics activation parameters, Ea, ∆Ha, and ∆Sa for the dissolution and passivation processes are deduced and discussed.