The density functional theory within generalized gradient approximation (GGA) has been used to calculate lattice parameter, total energy, phase transition pressure and electronic properties of neptunium sulphide (NpS). From our calculations we observe that NpS is stable in NaCl – type structure under ambient pressure. For this compound, the phase transition pressure was found to be 29.5 GPa. The nature of metallic behaviour is remarked from energy band diagram in NpS. All properties obtained for this compound are in good agreement with available results.