This study examines the phenomenon of the rivalry (competition) between legal principles and its impact on the rule of law in a state during armed conflict. For this purpose, the Ukrainian experience was investigated as a case due to the war in Ukraine, which was provoked by the aggression of the Russian Federation in 2022. The research scrutinises different legal acts that were adopted during the wartime in Ukraine and the responses to them by the authorities that are allowed to apply law. The author proceeds from the assumption that behind each legal norm, in its foundation, there is a principle of law or a set of them that manifest themselves through legal norms when they are applied in a specific situation. Each principle of law is formulated as an absolute, and each of them tends to its own self-absolutization.The only restraint on the self-absolutization of a principle is another principle of law. The study shows the difficulties and consequences of rivalry between legal principles. The situation of the rivalry between legal principles can be identified only in the process of the application of law and is characterised by the circumstances that lead to the necessity of choosing which principle of law should be upheld in a certain situation. This situation must be prevented by the inspection of the preconditions to it in law and the practice of the application of law. The rule of law in a state is negatively affected by the rivalry between legal principles. The paper also highlights the problems that agencies authorised to apply the law face in cases of rivalry between legal principles and a lack of statutes’ or courts’ clarifications in this regard. Therefore, a concrete mechanism for balancing the principles of law in the situation of their rivalry must be practically implemented.