Тhe article deals with the distribution of monosyllabic and two-syllabic endings of Instrumental singular case -ой(-ей) // -ою (-ею) and -ью // -ию in the language of different Pushkin’s prose genres: fiction (“Dubrovsky”, “Captain’s Daughter”), historical and journalistic works (“The History of Pugachev”, the papers on literature and theater), Pushkin’s letters to his wife. It finds out that the distribution of these endings in Pushkin’s prose of different genres is not similar (except for the forms of personal pronouns, where archaic two-syllable endings are used in all texts). In historical and journalistic prose two-syllable endings with sporadic penetration of monosyllabic as facultative variants are dominated. On the contrary, in Pushkin’s letters to his wife monosyllabic endings are preferred. At the same time monosyllabic and two-syllabic forms are no less common in attributive combination. In Pushkin’s fiction, however, there is a clear tendency to introduce at least one monosyllabic ending (most often in preposition attributive phrases) in constructions with several forms of Instrumental case for syntagmatic “facilitation” to create a certain quantitative balance.