Abstract: In international law, jus cogens is accepted as rules which override other rules of international law, be they conventional or customary. In this respect, it is problematic whether jus cogens also override the rule of State immunity. As it were, the question is if it is possible to grant State immunity to actions brought against a foreign State before a national court in case where the foreign State violated jus cogens. As to this question, the Italian Corte di Cassazione, Greek Areios Pagos and English House of Lords respectively took different positions. The English court took the view that, on the exception to the State immunity, the English State Immunity Act provides so cleary that the English court whose principal duty is to apply the Act of Parliament should be bound by the terms of the Act. Thus, the English court ruled that State Immunity Act does not have a provision to exclude granting State immunity in case where a foreign State violated jus cogens. And also, the English court decided that there is no conflict between jus cogens and the rule of State immunity based on the assumption that the first is in nature substantial, the second procedural. However, the Greek court decided that an act which violates jus cogens is international crime which cannot benefit from State immunity. The Greek court furthermore said that a foreign State which violated jus cogens waived the benefit of State immunity tacitly. Finally, the Italian court straightforwardly ruled that as jus cogens overrides the rule of State immunity, it is not allowed to grant State immunity to a foreign State which violates jus cogens. In spite of these diverse views on the content of State immunity, ICJ, in the case which was raised by Germany against Italy, endorsed the English view. I presume that the view of ICJ is reflecting the formal legal positivism according to which jus cogens and the rule of State immunity cannot conflict each other, because the one is substantial and the other procedural. But, I would like to argue that if the international community accepts jus cogens, then it is requested to grant full effect to jus cogens, which means that if the rule of State immunity acts as a bar to realize the value which is enshrined in jus cogens, then, the rule of State immunity yield to jus cogens.