Madiation as one of conflict resolution tool needs neutrality as its prerequisite. Neutrality is needed to guarantee that the third party does not have any vested or national interest. Vested or national interest of the third party will affect the mediation and the negotiation will not reach the best result for each parties. In this case neutrality cannot be fulfilled by United Nation in Morocco-Western Sahara negosiation and this is become stalemate in resolving conflict between Moroco and Western Sahara. This paper will examine why UN cannot play as neutral mediator in this negotiation.