"During the processing of the nickel-copper-cobalt ore of one of Russian deposits by classic technology it is expected to produce converted matte, with following chemical composition, wt. %: 60-68 Ni; 7-9 Cu; 4-6 Fe; 2-3 Co; 21-23 S. On model sample with the following composition, wt. %: 62 Ni; 7.1 Cu; 3.7 Fe; 2.2 Co; 18 S, were found, that leaching under pressure of oxygen characterized by a number of advantages in front of atmospheric leaching. This was evidenced by two parameters:Under atmospheric conditions, the process lasts 4-8 h (in comparison with 1.3-1.5 h in autoclave).Under increased pressure of oxygen achieved high rate of extraction of valuable components (wt. %: 67 Ni; 99 Cu; 99 Fe). Using special programs of experimental design made possible to examine more accurately influence of oxygen pressure and temperature on result of pressure leaching of nickel and also to establish more efficient process parameters. Flotation separation of such converted matte seems ineffective due to the low copper contents. Copper and nickel separation was carried out by using selective pressure leaching of nickel from converted matte. It was found that initial concentration of sulfuric acid has significant effect on the result of the selective extraction of nickel from the copper-nickel converted matte. Nickel extraction into solution was up to 50-55%, while approximately all amount of copper and iron was concen- trated in the cake (concentration in the final solution was, mg/l: 0.06 Cu; 0.62 Fe). Ways of processing leaching products were suggested."