The article highlights the life and scientific achievements of Olexandr Tverdokhliebov (historian, ethnographer, writer, teacher, member of the Kharkiv Historical and Philological Society, archivist of the Kharkiv Historical and Philological Society, member of the project of the Ministry of Finance of the Russian Empire, dedicated to various studies activist, member of the Okhtyrka Enlightenment (1917–1918), whose scientific work on the history of Sloboda and Left-Bank Ukraine still remains on time and which significance of works for historical and regional scientific research on the history of Slobidska Ukraine. The manuscripts of the researcher, which are stored in the funds of the Okhtyrka Museum of Local Lore, archival institutions, confirming the exceptional importance of works for historical and regional scientific research on the history of Sloboda Ukraine, which are published and currently important nowadays. The historical essay «City of Akhtyrka» describes all aspects of life of the inhabitants of the provincial Slobozhansk city in Kharkiv province in the XIX century, where the author delinetes the historical and geographical features of the city, its physical and geographical characteristics, settlement history and version of the origin of the city name. The industrial development of the city of Okhtyrka is illuminated in the work «The fate of the tobacco factory, established under Peter I in Akhtyrka», where the historian described the socio-economic and production conditions of tobacco growing and tobacco production. In the research and description of Orthodox parishes, churches and monasteries of Okhtyrka district of Kharkiv province, which are described in the work «On the history of Skelsky monastery». The author showed the formation of the monastery economy, in particular, its land tenure, which was an extremely important issue for the monastery, which was associated with the names of famous in the Left Bank of Ukraine family Shimonovsky, Hetmans I. Mazepa and I. Skoropadsky. The creative work of the historian includes explorations dedicated to Kotelevshchina, where the author provided information about the geographical location, socio-economic development of the region; archaeological monuments, features and descriptions of Kotelva buildings. Tverdokhlebov's ethnographic studies for the purpose of collecting folklore material became the basis of scientific ideas, methods of collecting ethnographic materials.The researcher managed to record many songs, thoughts of blind people, lyre players, bandura players of Okhtyrka district, which were written from lyricists Glushchenko and Gordienko. Ethnographic explorations became the basis for writing the works «Old World Carnival», «Popivna», «From the Past and Present Povorsklania» and others. O. Tverdokhlebov as a participant in the project of the Ministry of Finance of the Russian Empire, which was devoted to the study of handicrafts in different regions, studied pottery, leather, blacksmithing, sailing of several districts of Kharkiv province, the results of which were published in the third issue «Proceedings of the Commission for the Study of Handicrafts of the Kharkiv Province of Akhtyrsky District» 1885,where handicraft tools and means, living and working premises of craftsmen of Boromlya, Okhtyrka, Kuzemin, Kotelva and other settlements were illuminated and demographic characteristics of artisans (marital status, surnames, etc.) were described, also economic side of crafts and many other important issues that contribute to an objective assessment of the then state of folk crafts in Slobozhanshchina were outlined. The researcher focuses on the economy, culture, life, handicrafts, education, spiritual heritage of Slobozhanshchina, which are reflected in the work of the scientist «Hereditary Colonel», «Akhtyrka city», «Kotelva», «The fate of the tobacco factory founded by Peter I in Akhtyrka», «Century of Akhtyrsky district school (1790 – 1890)», «Akhtyrsky district on the eve of the XIX century» etc.