The article studies the linguistic features of the poem "Ana v ugyl" ("Mother and Son"), which is a coeval of the poem "Kyyssai Yusuf" by Kul Gali (the 11 th century). Several little-known sources of this work have reached us. We have introduced them into scientific circulation. The novelty of this work lies in the fact that we have carried out a comparative analysis of the lexical composition of these works, studied their isogosses, and the features of local beliefs. Based on the identified internal relationship, the article proves that both works belong to Bulgar-Tatar literature. The discovered linguistic facts indicate the uniformity of the literary language norms of the Bulgar-Tatars from the Middle Volga region. A comparative study of the works has made it possible to reveal the features of the original literary-fictional koine of the Tatars' ancestors who lived in the Middle Ages.