As pyrrhotite either dilutes nickel concentrates when recovered or causes significant metals loss and potential environmental harassments if discarded, production of separate pyrrhotite concentrate was thought as a reasonable alternative; however, processing it presents a challenge. A new process was studied to upgrade nickeliferous pyrrhotite concentrates using aqueous pressure oxidation under mild conditions, followed by sulfide precipitation and flotation. The effects of operation parameters such as oxygen pressure, temperature, initial acidity, retention time and concentrate composition were investigated. Pyrrhotite was found to be readily converted into iron oxide. The metal values present in the concentrate, principally nickel and copper, were dissolved in part as pyrrhotite was oxidized, then precipitated from the pulp as sulfides and finally recovered by flotation as a much higher grade concentrate with unreacted sulfide minerals and the produced elemental sulfur together. The pyrrhotite reporting to the leach residue as iron oxide was thus rejected in the flotation tailings.