This research aims to study and analyze one of the major projects of economic development through the adaptive reuse of old buildings in the historical districts in one of the major capitals in the world in London, UK, it is a project to develop and upgrade King's Cross. This research deals with presenting, analysis and extrapolation of the phases of the development of the region and the exploitation of it for tourism, commercial, leisure and educational activities in order to deduce ways of good exploitation to achieve economic returns from historical buildings in old districts for major investors participating in the project and the society, As well as tourism and cultural returns to preserve the history of the region and its identity and urban fabric. This Research conclusions and recommendations may be useful in the development and historic districts upgrade in our old heritage cities.