The article proposes a comprehensive analysis of the problem of rationality of law and rights as conceived by the great Romanian thinker, philosopher and lawyer Mircea Djuvara during the interwar period. In this context, the thinker’s views on the rational foundation of the legal phenomenon, the foundation of positive law through its reference to rational law, the formulation of logical principles of legal knowledge, the demonstration of the indispensability of rational law in legal systems are presented and analyzed. The common logical structure and common ethical foundations of law and morality, which in fact served as the basis for the formulation of the concept of rational law, are analysed. The mechanism of formation of general legal rules, which form the content of rational law, is identified. It also argues the implications of rational law both in the process of lawmaking and in the process of applying the rules of positive law.