Ni doped ZnS nanopowders were synthesized by hydrothermal method. The as-synthesized ZnS nanopowders possessed zinc blende structure with the particle sizes of similar to 20 nm, and they display a broad emission band from 400 nm to 700 nm centered at similar to 540 nm. The influence of Ni2+ doping and vacuum annealing on the structure, morphology and optical properties was investigated systematically. The results revealed that the emission peaks are blue shifted with Ni2+ doping, and the emission peaks of 0.2, 0.4, 0.6, 0.8 and 1.0 mol% Ni2+ doped ZnS nanopowders are centered at similar to 520, similar to 510, 500, 490 and 470 nm, respectively. While, the zinc blende phase transformed to wurtzite phase when annealing at 600 degrees C or higher, and the annealed samples exhibited three emission peaks positioned at similar to 490, similar to 547 and similar to 580 nm. The results indicated that the as prepared Ni2+-doped ZnS nanopowders have a potential application in LED as light conversion layer. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.