Constantine of Prselav’s Uchitel’noe evangelie (‘Didactic Gospel’) is a corpus of 51 sermons translated from Byzantine Greek and is one of the most important Bulgarian written monuments of the 9^th and 10^th centuries, not only among the translated but also among the original works, as it contains some parts composed by the translator himself. Some of the philological aspects of this codex, however, have not yet been systematically studied from all the philological aspects – e.g. as a lexical corpus or in terms of translation techniques used. The aim of the project will be to fill in a significant gap in the knowledge of the Bulgarian vocabulary of the time and more precisely of one of its prominent representatives. Its main task is to develop Old Bulgarian-Greek and Greek-Old Bulgarian word indices which should fully systemise the lexicon of this voluminous collection. The complete excerption of the data and their representation in the two glossaries will enrich the awareness of the language of Constantine of Preslav as both translator and author. The analysis of the data gathered in the bilingual dictionaries juxtaposed to those from other works of the time – as well as in the context of the Old Bulgarian lexis as a whole – will cast new light on the place of Uchitel’noe evangelie in the development of the literary Old Bulgarian language and will increase our knowledge about the lexical peculiarities related to the style of the author and the style of the genre. The work with both edited and manuscript Byzantine sources will probably lead to the discovery of closer correspondences of fragments with hitherto no exact parallels.