The effects of vanadium (V) dopant on the electronic and magnetic properties of monolayer MoS2 are investigated by first-principles calculation. The substitutionally doped V produces antiferromagnetic (AFM) or ferromagnetic (FM) states depending on the separation between V dopants. When the separation between V dopants is smaller than 6.38 angstrom and the maximum dopant concentration is 25%, the superexchange interaction between V atoms is stronger than the double exchange interaction between the localized V 3d orbitals and Mo 4d orbitals, resulting in the AFM state in monolayer MoS2. However, the double exchange interaction between the V and Mo atoms becomes stronger than the superexchange interaction between V atoms if the separation between V dopants is larger than 9.57 angstrom when the maximum dopant concentration is 11.11%. Consequently, the FM state is observed from the monolayer MoS2 and 100% spin polarization takes place if the separation between V atoms is further increased to 12.76 angstrom at a dopant concentration of 6.25%. The results suggest potential applications of monolayer MoS2 as diluted magnetic semiconductors (DMS) in spintronics. (C) 2017 Elsevier B.V. All rights reserved.