The paper is devoted to the study of the development of the adversarial principle in the criminal procedure of the Ukrainian SSR. In its development, the adversarial principle went through two stages. The first stage is characterized by the abolition of the main elements of adversariality introduced into criminal procedure by the judicial reform of Alexander II. The adversarial principle itself was criticized as bourgeois and alien to Soviet legal proceedings. After the adoption of the first Soviet criminal procedure acts, the criminal process, at least at the stage of trial, began to include adversarial elements. As for the preliminary investigation and inquiry, there were significant deviations from the requirements of the law, and in some cases the legislation itself created preconditions for actual arbitrariness and repression, and made it impossible for citizens of the Ukrainian SSR to defend their rights and interests or prove their innocence. In general, the process was in fact similar to an inquisition. Starting in the 1960s, criminal procedure legislation underwent significant changes in the direction of expanding individual rights and democratizing the process, which marked the beginning of the second stage. The adversarial nature of the procedure was no longer merely declarative, but became part of the mechanism for ensuring fairness during the trial. It began to act as a tool aimed at balancing the interests of the state and the interests of the persons involved in the process. The main goal of adversarialism was to ensure the impartial and independent administration of justice. In the context of criminal proceedings, adversarialism allowed the parties to defend their interests and present evidence before a neutral court, which undoubtedly contributed to the gradual establishment of the right to a fair trial in the country. At the same time, the adoption of the Criminal Procedure Code of the Ukrainian SSR in 1960 did not lead to the division of functions in criminal proceedings and did not introduce sufficient guarantees to ensure that the accused and suspects enjoy the full range of rights to defense against accusation and suspicion. The priority was not the competition between the parties, but the achievement of the objectives of socialist justice and the activities of state bodies (preliminary investigation, prosecution and court).