Abstract: The object of this study is the diaries of the Russian Successor and Grand Duke Michael Alexandrovich for 1899-1903. The subject of the research is the information potential of the diaries for the quantitative and qualitative expansion of the exposition dedicated to Grand Duke Michael Alexandrovich in connection with the process of museification of the historical building of the former Perm hotel "Korolyov's Rooms". The article examines the contents of the diaries of the Successor, pays special attention to the records of the Grand Duke, which allow to reveal such sections of the exposition as the family environment and daily life of Grand Duke Michael Alexandrovich, his places of residence, educational training, military, state and public activities, foreign trips. The method of source analysis allows us to identify the features of the diaries of Grand Duke Michael Alexandrovich in the context of the historical epoch and the personal characteristics of the author, to isolate the thematic headings necessary for the formation of the exposition in the text of the document. The diary entries of Grand Duke Michael Alexandrovich for the period when he was the Successor to the Russian throne are being prepared for the first time as materials for a museum exhibition. Based on the diaries, it becomes possible to show through the prism of the hero of the exhibition his family ties. The features of Grand Duke Michael Alexandrovich's daily life and everyday life in the Gatchina Palace and other residences, his interests and hobbies, trips around Russia and abroad are revealed. In various details, it is possible to show the military service of the young Successor, his participation in the activities of the highest state institutions of the Russian Empire, public service as a patron and trustee of various institutions.