Hydrometallurgical treatment of copper sulfide ore is increasingly establishing itself as a feasible route for the extraction of copper and recovery of associated precious metals value. This is attributed to the merits of this route, which include suitability for low-grade and complex ores, high recoveries, competitive economics, and other operational features. The leaching kinetics of Nigerian complex covellite ore was investigated in ammonia-ammonium sulfate solution. The concentration of ammonia and ammonium sulfate, the ore particle size, and the temperature were chosen as parameters in the experiments. The results show that temperature, concentration of ammonia-ammonium sulfate has favorable influence on the leaching rate of covellite ores; however, leaching rate decreases with increasing particle size. At optimal conditions (1.75mol/L NH4OH+0.5mol/L (NH4)2SO4, -90+75 μm, 75 °C, with moderate stirring) about 86.2% of copper ore reacted within 120 minutes. The mechanism of the leaching was further established by characterizing the raw ore and the leached residue by EDXRF - chemical composition, SEM - structural morphology and XRD - phase identification studies. From the X-ray diffraction analysis, the partially unreacted Cu and S phases were presumed to be CuO, and the iron present in the CuS phase was mainly converted to hematite (Fe2O3·H2O), as the CuS phase disintegrated and remained in the residue afterward.