The electronic structures and magnetism of N-doped ZnS are investigated using the full-potential linearized augmented plane-wave (FLAPW) method. We find that an isolated N atom produces a total magnetic moment of 1.0 mu(B) and introduces spin-polarized 2p states in the band gap. Several doping configurations studied suggest the existence of ferromagnetic coupling between N atoms. The long-range ferromagnetic order in N:ZnS system is mainly driven by N-Zn-S-Zn-N coupling chain through the strong p-p interactions between N and host S atoms. (C) 2010 Elsevier B.V. All rights reserved.