The concept of Terrorism, which can also be described as collective acts of violence, is a problematic phenomenon that aims to convey the messages desired to be given to the society, individually or collectively, through the murder of innocent people. Illegal activities and violent methods of terrorist organizations negatively affect states in terms of political, social, economic, cultural and psychological aspects. That’s why, countries that have to fight against terrorist organizations prevent these countries from taking steps that will strengthen terrorist organizations, such as the financial flows of these countries and the recruitment of new members to the organization. In this context, in order to be able to fight against terrorist organizations that harm every aspect of the economic and democratic development of countries and for state institutions to develop strategies for this, psychological analysis of these structures will prevent the emergence of new organizations with a similar structure and the attempt to fill some gaps by separatist organizations. The purpose of this paper is "what are the main motivations in terrorist behavior?" is to answer the question In this context, the analysis of the study will be made by comparing the psychological motivations of FETO, which was among the international terrorist organizations both in the State of the Republic of Turkey and abroad, which turned into a terrorist organization from a service movement at the beginning, and the PKK, which was founded in 1978 as a separatist terrorist organization in its origin. In the research, descriptive technique, which is one of the qualitative data collection methods, has been use, and national and international literature review will be made on the subject. As a result of the findings, it had been reveal the aspects that the terrorist organizations in question resemble psychologically and differ.