The purpose of the article is to consider the morphological peculiarities of the system of the nouns in New Bulgarian translation of the “Catechismos” written by Theodore the Studite, which is a part of the manuscripts no. 1/154 kept in Odessa National Scientific Library. The subject of the research is the morphological specifics of nouns in Odessa copy of the “Catechismos” dating from the 18th. The morphological peculiarities of nouns is considered in the context of the formation of a linguistic norm, which allowed the combination with different intensity of linguistic means of several language systems functioning at the time (traditional Middle Bulgarian written language, Church Slavonic Eastern recensions, and vernacular language form). The analysis proposed in this paper presents the extensive system of cases, which does not reflect the real vernacular Bulgarian speech in the 18th; the specifics of the functioning of the gramemes of the case paradigm of masculine, feminine and neuter nouns in the singular and plural forms is analyzed. Usage case endings mistakes, which indicates their artificial nature, are considered. The lack of article of nominal parts of speech is noted; the predominance of compound declension form of the adjectives and participles over short forms is revealed; the relatively high frequency of use of active present participles is registered. The results of the study make it possible to outline some probable factors that determine the writer’s preference for using the linguistic tools of the so-called “bookish”, “traditional”, “archaic” writing systems. An another reason which to some extent explains he usage of case inflections in the text of this relatively late stage of the historical development of the Bulgarian language might be the use of East Slavic copies of the Studite’s sermons by the scriber. Еhe comparison of “Catechismos” copies of South and East Slavic origin is necessary for verification of this assumption, in which we see prospects for further research.