We study the pressure-induced phase transition of wurtzite ZnS using a constant pressure ab initio technique. A first-order phase transition into a rocksalt state at 30-35 GPa is observed in the constant pressure simulation. We also investigate the stability of wurtzite (WZ) and zinc-blende (ZB) phases from energy-volume calculations and Gibbs free energies at zero temperature and find that both structures show nearly similar equations of state and transform into a rocksalt structure around 14 GPa, in agreement with experiments. Additionally, we examine the influence of pressure on the electronic structure of the wurtzite and zinc-blende ZnS crystals and find that their band gap energies exhibit similar tendency and increase with increasing pressure. The calculated pressure coefficients and deformation potential are found to be comparable with experiments. (C) 2009 Elsevier Ltd. All rights reserved.