In　the　evidential　reasoning　approach　of　decision　theory,　different　evidence　weights　can　generate　different　combined　results.　Consequently,　evidence　weights　can　significantly　influence　solutions.　In　terms　of　the　＇psychology　of　economic　man,＇　decision-makers　may　tend　to　seek　similar　pieces　of　evidence　to　support　their　own　evidence　and　thereby　form　alliances.　In　this　paper,　we　extend　the　concept　of　evidential　reasoning　(ER)　to　evidential　reasoning　based　on　alliances　(ERBA)　to　obtain　the　weights　of　evidence.　In　the　main　concept　of　ERBA,　pieces　of　evidence　that　are　easy　for　decision-makers　to　negotiate　are　classified　in　the　same　group　or　＇alliance.＇　On　the　other　hand,　if　the　pieces　of　evidence　are　not　easy　to　negotiate,　they　are　classified　in　different　alliances.　In　this　study,　two　negotiation　optimization　models　were　developed　to　provide　relative　importance　weights　based　on　intra-　and　inter-alliance　evidence　features.　The　proposed　models　enable　weighted　evidence　to　be　combined　using　the　ER　rule.　Experimental　results　showed　that　the　proposed　approach　is　rational　and　effective.　©　2017　Elsevier　Ltd