This article examines the existence of mercenaries and PMSC in a war with the context of defending the sovereignty of a State from colonialism. There were some conventions that mentioned some regulations about mercenaries. Although the use of mercenaries for offensive actions was prohibited regarding the violation of the principle of chivalry in international humanitarian law, none of them strictly prohibit the existence of mercenaries and PMSC in the context of defensive. This article uses the normative juridical as the research method. The conclusion that can be inferred from the article is that the use of mercenaries, even in the context of defending the sovereignty of a State from colonialism, is not recommended. However, the use of PMSC can be an alternative option for urgent situations based on further consideration of the legal basis, history, and principles of international humanitarian law.