In leaching of heazlewoodite obtained by pretreatment of nickel matte, the effects of temperature and oxidant concentration on leaching rate of nickel were investigated and kinetic parameters for selected optimum model of leaching mechanism were calculated. Fixed amount of heazlewoodite, contained 100-160㎛ of particle diameter, was compressed to pellet shape and leached in a mixture of FeCl₃, FeCl₂ and HCl as oxidant. The leaching rate was faster at higher temperature but activa-tion energy for initial reaction was as low as 8kcal/mol, which indicates its low dependence on temperature. Stirring speed and ionic concentration of H⁺ and Fe²⁺ had no significant effects on the rate and that of Fe³⁺ had effect on initial rate only. The rate controlling step for nickel dissolution was judged to be the diffusion of nickel through the layer of NiS, reaction intermediate.