The term ‘hybrid war’ has not been defined in the public international law. However, it is commonly used in the media, by politicians and also by academics in scientific discourses.The article raises the question of whether it is justified to use the term ʻhybrid war’ in reference to the military conflict in Ukraine. The authors scrutinise to what extent the situation in Ukraine meets the criteria of a ʻhybrid war’. Therefore, they try to define the term and describe its distinctive characteristics. Then, successive developments in Ukraine are analysed and compared with the characteristics. The article focuses on the role of the Dontsk People’s Republic and Luhansk People’s Republic, and their dependence on the Russian Federation. According to the authors, they are examples of actions conducted by proxies – the so called proxy war. This is the most important proof of the hybrid nature of the conflict in Ukraine. The authors also consider the responsibility of Russia for the actions of these separatist republics and wonder how to prevent the consequences of this conflict.