Research objectives: This article is dedicated to preliminarily research and the publication of the decree of the Kalmyk ruler, Donduk-Dashi Khan (r. 1741–1761), assigning to Mustafa Hajji the position of the mufti of the Muslims – people which were dependent on Donduk-Dashi Khan – as well as the position of the qadi and zaisang of the Nogays. Research materials: The decree (dated to 1750) reached us as a copy from the nineteenth century which was kept in the private archives of Abd al-Rahman Umerov – the Tatar religious leader and enlightener who was active at the end of nineteenth and beginning of twentieth century. Cartographic and lexicographic sources were used as well as works on Turkic and Mongolian diplomacy. Results and novelty of the research: The legal status of the representatives of Turkic-Muslim subjects of the Kalmyk rulers and the methods of their administration were not studied sufficiently up to the present. This is a result of the small number of the documentary sources which have been thus far introduced into scholarly circles. The publication of this decree of Donduk-Dashi Khan will fill the gaps in our knowledge of this problem.