Analysis of cyberattacks on the critical information infrastructure of Ukraine, and the fact of its increased complexity and more sophisticated relevant tools show the engagement of unfriendly countries, especially such as the Russian Federation, in destructive activities in Ukrainian cyberspace: in fact, Ukraine has become a testing ground for new cyber weapons and malicious strategies. Considering the cross-border nature of modern cyber threats and the priority of the Euro-Atlantic course of our country, an important vector of the activities of the Security Service of Ukraine has been to establish effective cooperation with international partners in combating cyber terrorism and hybrid aggression in cyberspace. Having this in mind the Security Service of Ukraine has established and maintained a high level of cooperation with intelligence services and law enforcement agencies in Europe, Asia and North America, as well as with key international organizations such as NATO, the OSCE, the Council of Europe, the UNO, the GUAM and others. At the same time, the Security Service of Ukraine has recently taken a proactive role as an initiator of innovations in the field of regional and international cybersecurity in relevant organizations. The issues of international cooperation of the Security Service of Ukraine in the field of cybersecurity within the framework of international and regional organizations were examined by such Ukrainian experts as V. Petrov, V. Khlevytsky, S. Bondarenko, O. Klimchuk, S. Petrov, N. Tkachuk, D. Melnyk and others. At the same time, these works, according to the authors’ opinion, do not reveal the features of international cooperation between the Security Service of Ukraine and the relevant special and law enforcement agencies of the Organization for Democracy and Economic Development GUAM in the field of cybersecurity and countering cyber threats. Given that Ukraine has recently been the object of cyberattacks, the sources of which originate from the Russian Federation, the establishment of the GUAM Regional Cybersecurity Center in Ukraine will help to strengthen the cyber security capacity of GUAM member countries. Moreover, the operation of this centre in our country, taking into account existing strong international contacts of Ukraine with NATO, EU, Council of Europe, OSCE, will help to create additional mechanisms for GUAM member states to exchange best world practices in cybersecurity as well as combating cybercrime, to increase the level of expertise of GUAM member states’ experts in these fields and to help improve the Organization’s image on the international arena. In this regard the Security Service of Ukraine should support the possible deployment of the technological component of the Center on the basis of the GUAM Secretariat in Ukraine, with the purpose of establishing the educational processes, information exchange, as well as remote access of relevant state bodies of GUAM member states. The provision of core funding of the future Center should be worked out within the framework of GUAM’s international cooperation with the USA, Japan, the EU, etc.