The　magnetic　behavior　of　Mn-doped　β-Ga2O3　is　studied　from　first-principles　calculations　within　the　generalized　gradient　approximation　method.　Calculations　show　that　ferromagnetic　ordering　is　always　favorable　for　configurations　in　which　two　Mn　ions　substitute　either　tetrahedral　or　octahedral　sites,　and　the　ferromagnetic　ground　state　is　also　sometimes　favorable　for　configurations　where　one　Mn　ion　substitutes　a　tetrahedral　site　and　another　Mn　ion　substitutes　an　octahedral　site.　However,　the　configurations　of　the　latter　case　are　less　stable　than　those　of　the　former.　©　2008　Acta　Materialia　Inc.