The results of researches of nickel oxide (II) leaching with water solutions of sulfuric acid from semi-finished product of nickel production — roasted product of oxidizing roasting of sulphide nickel concentrate have been exposed. Nickel dissolving from the roasted product is possible at temperatures above 180 oC. It has been shown that speed of leaching have been raised and temperature has been reduced till 90 oC via implementation of oxidizing material in the pulp and maintenance of oxidizing-reducing potential on definitely level. The mechanism of sharp speed raising, based on possibility of forming of nickel oxides with the higher oxidation level (NiOx) in the roasting product has been proposed. The nickel oxide (II) can be dissolved through the stages of formation and follow dissolving of NiOx. The speed of both stages of this cycle process is more higher than speed of direct reaction.