The catalytic sulfide ion oxidation by oxygen to elemental sulfur over beta-Ni(OH)(2) and LiNiO2 has been studied. As a result of experimental investigation performed, a reaction mechanism is suggested which involves heterogeneous and homogeneous processes. Dioxygen activation in the heterogeneous process proceeds via a redox Ni2+ <-> Ni3+ transition and participation of OH- groups. The active HO2- species thus formed carries on the reaction in homogeneous phase. Nickel hydroxides are promising catalysts for practical application.