The principle of sovereignty is one of the most fundamental principles of organizing the internal and external life of the state. Studying the operation of the principle of sovereignty during the period of the Soviet Union (USSR) is particularly difficult given the sometimes conflicting assessments of this state-legal phenomenon. The article attempts to form a conceptual approach to the consideration of mechanisms for the implementation of the principle of sovereignty during the period of Ukraine’s stay as part of the USSR in the context of the state-legal processes of the middle of the 20th century. An analysis of Chapter 1 of the Constitution of the Ukrainian SSR of 1978, which established the results of Ukrainian Soviet state-building for 60 years and determined the foundations of the political system, gives grounds for asserting that there was an actual dichotomy in the organization of power: the Soviets were the nominal subject (carrier) of sovereignty, and the CPSU acted as its administrator. In fact, a state was created with two verticals of power - the Communist Party and the Soviet, when the exercise of power in the Soviet-parliamentary manner enshrined in the Constitution was actually an imitation of parliamentarism. Taking this into account, it was necessary to propose some conceptual approaches for researching the mechanisms of implementation of the principle of sovereignty in the Ukrainian SSR. It is argued that sovereignty is a qualitative, not a quantitative category, one of the characteristics of which is inalienability and indivisibility. At the same time, the sphere of exercising the sovereign rights of the state can be limited in acertain way (self-limited). The analysis of the constitutional norms of the Ukrainian SSR indicates a significant limitation of the material content - the possibilities and means of realizing sovereignty - due to the transfer to the union center of a significant range of fundamental sovereign rights, which, in turn, does not allow us to speak aboutthe Ukrainian SSR and other union republics as full-fledged states. On the other hand, there was the declaration of sovereignty and the realization of a certain part of sovereign rights, their formalization. Therefore, it can be argued that the sovereignty of the Ukrainian SSR is state sovereignty, which was ensured by the state-legal mechanism, had formal and legal grounds and itself was the basis for the realization of legal opportunities, which are recognized as inalienable, should be common and equal for every country, which she endows herself with her will. Their actual implementation became possible in 1991. The foregoing gives reason to consider the Ukrainian SSR (URSR) as an integral component of the integral Ukrainian state-building process, which was characterized by the establishment of formal and legal institutions and mechanisms, which allowed them to be used, in particular, in the implementation of the sovereignty of Ukraine as a Ukrainian national state. Key words: Ukraine, history of law, sovereignty, sovereign rights of the state, state-legal mechanism, state-making process.