Thermal expansion of nickel sulfide Ni3S2, phase transformations in the synthesized and industrial samples at heating in inert (1070 K) and oxidizing (1270 K) atmospheres are investigate by high-temperature X-ray powder diffraction, differential scanning calorimetry and mass - spectrometry methods. Temperature dependences of the lattice parameters a-Ni3S2 and p-Ni3ixS2 are determined, thermal expansion coefficients are calculated at heating in helium and on air. Chemism oxidations of nickel sulfide, including chemical adsorption oxygen, formation of nickel sulfate, oxidation Ni3S2 with allocation NiO and dioxide sulfur is offered.