In most of the contemporary political systems, the principle of separation of powers is recognized as an effective way for management of political and social affairs and as a fundamental principle in State constitutions. For explaining the significance of this principle, it is emphasized that the separation of powers is a guarantee for social security and preventing despotism. Regarding the role of this principle in the UN structure, assessing the relation between three pillars of the UN, i.e. the General Assembly, the Security Council and the International Court of Justice, it will be understood that although enforcement of this principle among these three organs can prevent the misuse of power dedicated to these organs, but this was not meant by those who established the UN charter and it is hard to speak about the existence of separation of powers in the UN system.