The Izmir Historic City Center, including Kestelli Street, is a multi-layered area that has hosted various civilizations throughout history, and contains a wealth of historical and cultural heritage. With the foundation of the Republic, the breaking points that emerged with the developments in history caused changes in many factors including commercial, social and demographic. In parallel with these transformations, the first steps were taken to preserve the region through the implementation of conservation and planning studies, which commenced in the second half of the 20th century. The aim of the study is to determine the physical transformations that occurred in Kestelli Street since the foundation of the Republic of Turkiye by considering diverse aspects of it in various periods. Within the scope of the study, the transformation of Kestelli Street in the last 100 years within the framework of Izmir history and planning studies has been analyzed in four periods by examining old maps, aerial photographs and old documents and using a comparative method. Kestelli Street is examined within the context of urban planning and registration decisions, solid-void rate, landuse, lot organization, storey system, construction techniques, conservation status, and architectural elements. The objective is to illuminate the transformation of the city from the past to the present, to determine the changing economic and social factors, and to assess the impact of urban planning studies on the city. The results of the analysis conducted in the area indicate that uncontrolled practices that do not respect and damage the values of the region have continued to increase in recent years. This has led to a situation in which Kestelli Street is under threat of losing its historical, architectural, and social values. The protection of Kestelli Street as a whole is of great importance in terms of safeguarding the city's identity and cultural heritage for future generations. In this framework, the data collected within the scope of the study is intended to serve as a foundation for subsequent planning and conservation studies