Reaction of nickel chloride with sodium dithionite in aqueous solutions at ambient temperature has been investigated systematically to obtain nickel sulfides. The products are characterized by X-ray diffraction, thermogravimetric analysis, and electrical resistivity and magnetic susceptibility measurements. It is found that the compositions and structures of the products are controlled by the reaction pH and the amount of the reactants. While reactions under highly acidic (pH less than or equal to 2) and basic (pH greater than or equal to 7) conditions yield crystalline sulfur and amorphous or poorly crystalline NiySx, respectively, those at intermediate 3 less than or equal to pH less than or equal to 6 give crystalline NiySx. Both crystalline Ni3S2 (heazlewoodite structure) and Ni3S4 (spinel structure) have been obtained at room temperature. Additionally, NiS (millerite structure) is obtained by carefully heating Ni3S4 at 200 degreesC in a mixture of 90% Ar and 10% H-2. Ni3S4 is found to be metastable, and it begins to disproportionate above 100 degreesC. Both Ni3S2 and Ni3S4 show metallic behavior. While Ni3S2 exhibits temperature-independent magnetic susceptibility, Ni3S4 shows ferrimagnetic ordering below 20 K.