This article analyses if and in which direction investment tribunal in intra-EU investment arbitration would apply EU law and if it could at least take it into account by decision making process. It considers three approaches in which EU law and its rules could be relevant. First, EU law is a system based on international treaties, and is therefore a part of international law Second, in consequence of the doctrine of direct effect, rules of the EU law automatically become a part of legal orders of member states, and from the point of view of investment tribunal these rules are part of the legal order of host state. Third, EU law can be in international investment arbitration relevant as a fact.