The purpose of this article is to determine the word-formation and lexico-semantic features of the designations nomina agentis and nomina actoris registered in Theodore Studite’s «Small Catechism» and to consider these linguistic units as a means of archaization or modernization (approximation to colloquial language) of the text. The subject of the study is the word-formation and lexico-semantic features of the nouns nomina agentis and nomina actoris. The Odesa copy of the «Small Catechism» is included in collection No. 1/154, kept in the Odesa National Scientific Library. All recorded nouns of nomina agentis and nomina actoris divide by origin into two groups: native Slavic language units and borrowed ones; indigenous Slavic lexemes in each nominative series distribute into groups according to word-formation types. Within word-formation types, lexico-semantic groups are distinguished. The separation of two lexico-semantic groups — names of individuals by type of activity, nature of occupation, profession, and names of individuals by their characteristic principles of behavior — is possible for each word-formation type. The separation of other lexico-semantic groups is optional. It has been established that for Slavic designations of nomina agentis, the most productive wordformation formants are -тел, -ник, -ец, unproductive ones are -ица, *-jь, and singular -ач; for the formation of designations of nomina actoris the affix -ник is most often used, very rarely -ар. The known stylistic differentiation between the literary affix -тел and the affixes -ник, -ец, which could participate in the creation of both literary and colloquial elements, does not implement in the «Small Catechism». The results of the study allow us to conclude about a number of factors that could cause this phenomenon. The main of them are features of the content of sermons, individual perception of the language norm by the scribe working on the text, his approach to the selection of vocabulary, and orientation to the specificity of the audience — well-prepared and educated church ministers, monks. Borrowings are represented only by Hellenisms, most of which were assimilated in ancient times. Prospects for further research we see in specifying the role of the Church Slavonic language of the Eastern edition in the productivity of these word-formation types.