This paper discussed the relation between Coercive Diplomacy and International law through International Institutions. After a brief review on the history and the mechanisms of Coercive Diplomacy and International Law, the means of Coercive Diplomacy in the after Second World War era is introduced. And the ways in which the Super Powers abuse the International Courts and Organizations to pressure other states is explained. International Organizations Functions inter alia, legitimating the Coercive Diplomacy is investigated. This legitimating and justifying role of International institutes is elicited by analyzing the UN Security Council decisions and International Atomic Energy Agency resolutions related to Iran Nuclear Crisis. Also Sanction as an alternative tool to Use of Force in the post-Cold War Coercive Diplomacy is perused and some examples of it are given.  The conformity of the UN Security Council decisions to International Law is studied in the European Court of Human Rights (ECtHR) and European Court of Justice (ECJ) cases. The last part is dedicated to summarize the conditions of an efficient and successful Coercive Diplomacy.