The Lithuanian language is a typical flectional language that has a very sophisticated system of grammatical forms and many means of derivation; it is also characterized by uncertain boundaries between morphemes. All this makes the morphemic analysis of the Lithuanian language very complex. The aim of this research is to define and describe morphemic structural models of inflective parts of speech (i.e. nouns, adjectives, numerals, pronouns, and verbs) and regularities of their usage in contemporary Lithuanian.