In this study, the effects of acid/ore ratio (0.1-0.6 g H2SO4/g dry ore), leaching temperature (200–240 °C) and leaching time (30–120 minutes) on the high pressure sulphuric acid leaching of a lateritic nickel ore sample having 1.37% Ni, 0.076% Co and 47.72% Fe2O3 were investigated. The leaching experiments showed that the increase of leaching temperature and leaching time increased continuously the amount of dissolved Ni and Co, and decreased continuously the amount of dissolved Fe from the lateritic nickel ore sample. With the increase of acid/ore ratio, dissolution ratio values of Ni and Co increased up to acid/ore ratio of 0.3, and above 0.3, lower dissolution ratio values were obtained. Although leach residues obtained after leaching at acid/ore ratio of 0.3 contained mainly hematite, quartz and anhydrite, the use of higher amounts of acid (e.g. 0.6) caused the formation of basic ferric sulphate, verified by the sulphur contents and the X-ray diffraction patterns of leach residues. The dissolution ratio values of 86.4%, 92.8%, 95.1% and 96.6% Ni were obtained after 30, 60, 90 and 120 minutes of leaching, respectively, at acid/ore ratio of 0.3 and leaching temperature of 240 °C. In this study, the leaching behaviours of Mg, Ca, Mn, Al and Cr were also determined.