Very pure nanocrystalline hexagonal nickel sulfide phase (h-NiS) were produced by the solventless route in air at temperatures of only 190°C. Only the cubic NiS2 nickel sulfide phase is obtained when the sulfur source reacting with the nickel acetate powder (NiAc) is exchanged from thiourea (TU) to elemental sulfur (SN). Phase mixture of h-NiS, NiS2 and Ni3S4 with less aggregated particles was obtained when using both TU and SN sulfur sources. Relative concentrations of the phases were quantified by Rietveld refinement of the XRD powder patterns. The thermal evolution of stoichiometric reagents mixture was observed by TG-FTIR and DSC curves.