The paper analyzes information about the Qara-Khitais and the Mongols of Genghis Khan’s era contained in the big “universal” encyclopedia of geographical, historical and philosophical sciences of the Medieval Muslim East entitled “The limit of desire in literature diversity” (“Nihayat al-arab fi funun al-adab”in Arabic). It was written by an Arabic (Egyptian) scholar of the late 13th – early 14th centuriesShihab al-din al-Nuwayri. The author triesto reveal the Arabic scholar’s methods of work with his sources of information. The analysis of two fragments of al-Nuwayri’s encyclopedia shows that in reconstructingthe historyof the Qara-Khitais and the Mongols of Genghis Khan’s eraand working with the sources, al-Nuwayriused the critical method. Among his sources, there were Ibn al-Athir’s great historical chronicle entitled “al-Kamil fi al-ta’rikh” (“Full historical [corpus]”) and al-Nasawi’s biographic work“Sirat al-sultan Djalal al-din Mankubirti” (“The biography of sultan Djalal al-din Mankubirti”) that most substantively described the history of the Qara-Khitais and the Mongols.
Key words: source, method, al-Nuwayri, encyclopedia, Qara-Khitais, Mongols, Genghis Khan.