The article offers a comparative analysis of the category of number in different structural languages: Russian and Kituba. It considers the place of these languages in the genealogical classification. The authors consider the purpose of this article to describe the same and different ways of expressing the category of numbers in the significant parts of speech in Old Russian and Russian, in Kikongo and Kituba, in modern Russian and Kituba. Special attention is paid to the category of number in significant parts of speech, the words singulariatantum and pluraliatantum are studied, and cases of discrepancies in the formation of singular and plural forms in these languages are described.
Key words: multi-system languages, number category, suppletion, singulariatantum, pluraliatantum, inflectional, agglutinative, genealogical classification, contrastive linguistics, Kituba language.