The paper examines the problem of the militarization of outer space, the relevance of which has significantly increased in recent years in connection with the termination of a number of important international treaties in the field of arms reduction. The problem is aggravated by the absence of a complete ban on the placement of weapons in outer space in international treaties. The paper analyzes the norms of international space law, the norms of the 1959 Antarctic Treaty, doctrinal approaches to determining the use of outer space for peaceful purposes. The author concludes that the terms “peaceful use” and “use exclusively for peaceful purposes” in relation to outer space have different meaningful boundaries: the first reflects an interest in peaceful uses (non-military) without establishing a complete ban on the use of outer space for military purposes, the second excludes any purpose other than peaceful. In order to exclude the use of outer space for military purposes the author proposes to use the second term. The use of military means for peaceful purposes is permitted in international law; therefore, it is proposed to establish the legal limits of such use in outer space, clearly defining the prohibited activities. The author notes that at present the principle of the use of outer space for peaceful purposes is a guideline reflecting the desire of the international community to prevent the use of outer space for military purposes.