Architectural structures, which are important witnesses of changing times, become important elements of tangible cultural heritage by continuing their existence over time. These artifacts are documents that keep a record of the changes that constitute the collective memory of the society in the geography where they are located. The built environment, which is shaped in the dialectics of complex relations in social life, sheds light on the history, culture, social and economic life of the communities that are active in the process, and their orientations in many areas, especially. This situation affects the tangible and intangible cultural values of communities with different religions and cultures sharing the same geography throughout history. These impacts include construction and destruction activities as well as transformation. These transformations have been frequently applied throughout history, regardless of time and geography, depending on the needs brought about by political relations, political patterns, and social changes. In the Ottoman Empire, churches were converted into mosques due to their physical manifestations of conquest, changes in the demographic structure of the conquered region over time, and the need for the reuse of the structures. Considering the activities of conversion from church to mosque, Trabzon province emerges as an important city with its building stock. From this point of view, the study focuses on the buildings that were converted for various reasons after the Ottoman conquest of the city (1461-1923) and that serve as mosques today. The aim of the study is to reveal the spatial changes experienced by the converted mosques after the change of function. The transformation processes will be analyzed by determining the similarities and differences in the functional, functional, and spatial changes of the buildings during their conversion from church to mosque. Thus, it is aimed to contribute to the reduction of the margin of error by using the analysis data obtained in the transformations of religious buildings that will undergo function changes within the scope of various needs and/or obligations in the future and to contribute to the preservation of tangible and intangible cultural heritage values inherited from the past by transferring them to future generations. Keywords: Mosque, Church, Converted, Ottoman, Trabzon.