Adapting a historical building that cannot preserve its original function to reuse suitable for its architectural character is an accepted approach in terms of contemporary conservation theory. If a building can no longer serve the purpose for which it was built, when it is adapted to the new function, the building will be sustainable and livable by ensuring the continuity of the structure's function.Kostaki Mansion is one of the buildings that cannot preserve its original use. The mansion, which was built by Banker Kostaki Teophylaktos in Trabzon between 1898 and 1913, has a special place in the architectural history of the country with its construction system differing from the traditional, facade layout, planimetric feature, intense decoration, and ornament program. The Kostaki family came to Trabzon in the 1890s and moved to the mansion in 1913 after the meticulous construction and decoration work carried out in the building was completed. However, during the Russian occupation, the mansion was turned into the headquarters of the Russian army and the family had to leave their home. The building, which was adapted to different functions in the later process, is used as a museum today. The interventions made to adapt the building to the different uses have caused significant material and structural problems in the building. Within the scope of the prepared conservation project, preservation and strengthening interventions were developed that planned to extend the life of the building, respecting both the initial design and subsequent interventions of the building, which was used with different functions in the historical process.This research examines the change and transformation process of the Kostaki mansion, which could not maintain its original function, from the first construction date to the present, by dividing it into three chronological periods. In addition to the restitution periodization proposal, it is also aimed to share the documents that developed during the preparation of the restoration and exhibition projects with the researchers. No sponsor