Previous　studies　have　shown　that　ingroup/outgroup　membership　influences　individual＇s　fairness　considerations.　However,　it　is　not　clear　yet　how　group　membership　influences　brain　activity　when　a　recipient　evaluates　the　fairness　of　asset　distribution.　In　this　study,　subjects　participated　as　recipients　in　an　Ultimatum　Game　with　alleged　members　of　both　an　experimentally　induced　ingroup　and　outgroup.　They　either　received　extremely　unequal,　moderately　unequal,　or　equal　offers　from　proposers　while　electroencephalogram　was　recorded.　Behavioral　results　showed　that　the　acceptance　rates　for　unequal　offers　were　higher　when　interacting　with　ingroup　partners　than　with　outgroup　partners.　Analyses　of　event　related　potentials　revealed　that　proposers＇　group　membership　modulated　offer　evaluation　at　earlier　processing　stages.　Feedback-related　negativity　was　more　negative　for　extremely　and　moderately　unequal　offers　compared　to　equal　offers　in　the　ingroup　interaction　whereas　it　did　not　show　differential　responses　to　different　offers　in　the　outgroup　interaction.　Analyses　of　event　related　oscillations　revealed　that　the　theta　power　(4-6　Hz)　was　larger　for　moderately　unequal　offers　than　equal　offers　in　the　ingroup　interaction　whereas　it　did　not　show　differential　responses　to　different　offers　in　the　outgroup　interaction.　Thus,　early　mechanisms　of　fairness　evaluation　are　strongly　modulated　by　the　ingroup/outgroup　membership　of　the　interaction　partner.　©　The　Author(s)　2017.