When the original purpose of a heritage building is no longer adequate for its survival, the structure is adaptive reuse and continues to exist in the future. The transition of buildings into museums in the process of adaptive reuse is examined in this study. The study’s aim is to determine which design principles should be applied when heritage buildings are converted into museums. Literature research on the issue was conducted in the study, and the interior design standarts of museums, as well as the concept of conservation and adaptive reuse, were studied. In this regard, the examples of Istanbul’s Pera Museum, Dogancay Museum and Salt Galata, which have been converted into museums from heritage buildings, have been compared. In the research, which is a case study, the interiors of three museums were observed and analyzed. The interiors of the museums have been examined under many heading such as lighting, exhibition, circulation, security and accessibility. As a result of the research, it was determined that the heritage buildings that were adaptive reuse should meet the design criteria of the new function and design criteria were suggested. Adaptive reuse heritage buildings are examples of urban identity by preserving the qualities they had in the past.