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United Nations Charter, relying on historical events, absolutely prohibited the use of force in international law and relations. In spite of this, the need for predicting the cases of using force in order to keep international peace and security requires it that through systematizing the possibility of resorting to force and institutionalizing it within the system of the Security Council of the United Nations, the use of force be allowed in cases where the realities of the international community not only logically explains but also authorizes the use of force. Although the right of self-defense and the authority of the Security Council are the two exceptions contained in the UN Charter to materialize the mentioned goal, in recent decades, a concept, known as humanitarian intervention, has emerged, and has been considered by some states as the third exception to the principle of prohibition of the use of force. The question the present study asks in this regard is that if NATO's intervention in Kosovo War can be considered as legitimate within the definition of humanitarian intervention of the international law. Can one claim that a new tradition, or put differently, a new exception to the principle of the prohibition of resorting to force is being formed? The response to this question is that currently no exception to the aforementioned principle has been accepted under the title of humanitarian intervention. This article discusses the concept of humanitarian intervention and the legitimacy of such a claim.