Ancient ancestors of such sub-ethnic units of the Tatar nation, as Nizhny Novgorod Mishar Tatars (Nizhgars), in varying degrees, include: Madjars, Burtases, Kipchaks, perhaps the Khazars. The article examines some subjects related to the last three ethnic groups in the light of their relation to the ethnogenesis of Mishars. The article is explored to the theme of the Khazar influence on the Burtases, including possible penetration of Judaism to one of the Burtases tribes; listed the positive and negative sides of Kipchak theory of the Mishars' origin; studied in detail themes of Burtases. The author assumes Iranian origin of this people, which was turkified during the Khazar Kaganate and then entered the sphere of the Volga Bulgaria's influence. From the XII-XIII centuries Burtases moved North from its Central lands on the border of modem Mordovia and the Penza region. In the South of Nizhny Novgorod region arose Purgasova volost (principality), which estimated by number of authors as Burtases state entity, predecessor of Meshera yurt (govemorate) of the Golden Horde.