Ever since, international terrorism has always been a problem in international community. The aims of this study are to know the status of the law of terrorism based on international law along the analysis of whether a state can deprived someone’s citizenship who participated in ISIS terrorism. This study is a research of normative law using legilation approaches to analyse relevant international law instruments and concept approach. Based on the result, normatively, Indonesia currently cannot deprived someone’s citizenship who enrolled or participated in ISIS terrorism because Indonesia adheres to the principle of single citizenship which may cause stateless person. On the other side, sole ISIS terrorism network cannot be said as a state. According to International Montevideo Convention viz. Montevideo Convention on the Rights and Duties of States in 1933, ISIS is not an entity of a state. Indonesia cannot deprived someone’s citizenship who joined ISIS not merely by international legal fact that ISIS is not a state, but also based on Law number 12 year 2006 about The Republic of Indonesia’s citizenship, that is every Indonesia citizenship will be deprived if the person voluntarily makes an oath pr declares a pledge of allegiance to another country or part of another country. Whereas ISIS is not a state’s entity. It can be concluded that, normatively, Indonesian citizen who participated or enrolled themselves in ISIS terrorism cannot be deprived of their citizenship.