In this article, the author considers the concept of res judicata. It is concluded that res judicata has two main properties: presumption of the truth of the judgment, and prejudice. The author examines the presumption of the truth of the judgment, and prejudice arising from the concept of res judicata in relation to the decisions of the European Court of Human Rights. The author comes to the conclusion that the decisions of the European Court of Human Rights as res judicata have the property of a presumption in full measure. At the same time, due to the expanding competence of the Constitutional Court of the Russian Federation, the power of res judicata of the European Court of Human Rights may be limited. With regard to the second property of res judicata - prejudice, it is concluded that the decisions of the European Court of Human Rights res judicata do not have prejudice of evidentiary value. However, decisions of the European Court of Human Rights res judicata have the property of prejudicial competence of an international (interstate) agency. In this sense, according to the author, res judicata has an intersectoral prejudicial meaning.