Introduction. The history of the Chagatai Ulus and Moghulistan remains an understudied area of medieval historiography, which is nonetheless essential enough and can yield a lot to researchers engaged in exploring the history of medieval Genghisid states. And it is Majmu al-Tawarikh by S. Akhsikendi which proves a most valuable source on the theme, since it contains a wealth of historical knowledge on Eastern peoples of the thirteenth to sixteenth centuries, including Kalmaks, Kyrgyzes, Moghuls, etc. Goals. The study examines Majmu al-Tawarikh for data relating to the Chagatai Ulus and Moghulistan, attempts a comparative analysis of the manuscript and other available sources on the investigated states, and seeks to determine the value of the text for Oriental historical science. Materials and methods. The work focuses on published sections of the well-known translations of Majmu al-Tawarikh and Zafarnama. In addition, the historical reliability of the identified data has been verified via the epic poem of Edige, Materials in the History of Kazakh Khanates, and History of Kazakhstan from Persian Sources. The key research principles include those of historicism and systemicity, while the key research methods are the comparative historical and ideographic ones. Results. The paper examines Majmu al-Tawarikh and analyzes data pertaining to the past of the Chagatai Ulus and Moghulistan, provides a historiographic review to explain the significance of the source. Despite some scholars tended to criticize Majmu al-Tawarikh for a variety of revealed inaccuracies and phantasmagorias, they did recognize its certain value. Majmu al-Tawarikh mentions names of a number of khans and emirs of the Chagatai Ulus and Moghulistan — with reported coincidences or differences in other sources. The work sets forth and substantiates a hypothesis that Zafarnama (‘Book of Victories’) by Sharaf ad-Din Ali Yazdi may have been a fifth source for the author of Majmu al-Tawarikh. Conclusions. Majmu al-Tawarikh contains essential information on the history of the Chagataid states, as well as on the history of neighboring territories and peoples. However, the study of the obtained information should be approached critically, and it is urgent to compare the latter to related messages included in other sources. The introduction of the data into scientific discourse shall significantly expand and supplement contemporary historical knowledge on medieval Central Asian states.