This article is focused on one of the most puzzling questions of ethnic history of Bulgaria, the North Caucasus, Bashkortostan, and in general, the Eurasian steppes in the early medieval. In domestic and foreign science there is a sustainable idea that the term Burdzhan, used by Arab authors of VIII-XV centuries, signifi es the Danubian Bulgaria. Based on the information of Arabic, Byzantium, Armenian and Bashkir essays, author revises this provision. The study concludes that the Bulgarian kingdom and the Burdzhan principality existed at the same time in the VII- XIII centuries at Balkans, which led to the substitution of the above-mentioned terms. As follows from the analysis of the sources, the toponym and ethnonym Burdzhan, used by Arabs, in most cases referred to possession of the same name, not to the state of the Danubian Bulgars. Exceptions that occurred in the works of al-Idrisi, Ibn Khaldun and others can be explained, and they require separate consideration. The article covers history and ethnic attribution of Burdzhan Kingdom, that had existed in the Northern Caucasus in II-VII centuries, as well as the fate of its population after the Kingdom was destroyed in the result of devastating campaign of the Khalifat army during the Arabic and Khazar wars of the second half of VII century - fi rst third of the beginning of VIII century.