The article is devoted to the analysis of the content of such a principle of criminal proceedings as reasonable terms. The main criteria for determining the reasonableness of the terms are considered. The issue of observance of the principle of reasonable time in criminal proceedings is analyzed through the prism of the case law of the European Court of Human Rights. The principle of reasonableness of time limits in criminal proceedings occupies a prominent place among the list of principles, as it is an aspect of a person's right to a fair trial, provided for in Art. 6 ECHR. The peculiarity of this principle is that it is a novelty in the legislation, which was enshrined in the new Criminal Procedure Code in 2012. Article 28 of the CPC provides a definition of “reasonable time”, but it is formal and there are currently problems with its uniform enforcement. To ensure an effective mechanism for compliance with the reasonableness of deadlines in the current CPC of Ukraine prescribes such criteria as: 1) the complexity of criminal proceedings; 2) behavior of participants in criminal proceedings; 3) the manner in which the investigator, prosecutor and court exercise their powers.The European Court of Human Rights singles out a fourth criterion - the importance of the case to the applicant. This article will analyze the content of these criteria and the practice of the ECtHR regarding the violation by national authorities of the reasonableness of the terms of criminal proceedings. Possible ways to equal application of criminal procedural terms will also be suggested. Among them, amendments to the criminal law with clearly defined rules on the duration of criminal proceedings as a whole or its individual procedural actions, which in general will ensure the right of a person to a fair trial. Also, many countries already have adequate remedies for complaints of unreasonable length of proceedings within the meaning of Article 6 of the ECHR. Thus, in order to bring domestic law in line with the requirements of the Convention, Italy has a law passed on 24 March 2001, which introduces a legal remedy for resolving disputes concerning the "reasonable" length of proceedings at the national level. This way of solving the problem of unequal law enforcement can be introduced in Ukraine as well.