Electron-beam mediated substitutional doping of monolayer MoS2 was recently demonstrated, opening a new way to modify its properties. Using first-principles calculations, the structural, electronic and magnetic properties of monolayer MoS2 doped with nonmetal and transition-metal atoms are investigated. All dopants are strongly bound to the structures, inducing interesting magnetic behaviors. While all H, B, N and F-doped monolayers have magnetic moment of 1.0 mu(B), V, Cr, Mn, Fe and Co-doped ones attain 1.0, 4.0, 3.0, 3.0 and 1.0 mu(B), respectively. Additionally, MoS2 undergoes transition from semiconductor to half-metal in the presence of H, B or Cr doping. (C) 2013 Elsevier B.V. All rights reserved.