A study of urban built form is justified when considering the fact that metamorphosis in urban form brought up by human beings would affect human beings' life afterwards. This justification is especially obvious when change in urban built form is significant and radical. Beijing, China, is well-known for its historical city plan and architecture. Since the city became the capital of the People's Republic of China in 1949, it has undergone extensive reconstruction. Four decades have passed and the reconstruction has resulted in enormous changes in the built form of the city. As a historical city, the metamorphosis in the urban built form of Beijing involves demolition of the old built environments, preservation of the significant historical ones, and construction of the new ones. The change in the built form has effects far beyond built environment itself. By tearing down an old or erecting a new built environment, what disappear or comes about is not only physical entities, but also the meanings and values embodied in the physical entities. Using questionnaire survey and interview as well as on-site observation as the instrument, the authors conducted a study focusing on people's perceptions and evaluations of changing Beijing in 1987. Based on findings of that case study, this paper first illustrates people's reactions to the demolition and preservation of historical built environments and to construction the newly built modern ones. It then discusses lessons learned through the experience of Beijing regarding impacts of metamorphosis in urban built form on peoples city image and city life. As for the preservation of historical built environments, this study found that the public's attitudes towards those environments generally follow a trend from depreciation to appreciation when the historical environments become rarer and rarer. This trend is evidenced clearly by the public's changing attitudes towards the demolition of some historical environments such as the old city wall, and by importance of the historical environments in people's images of today's Beijing. Many well preserved historical built environments are among the most dominant elements in images of the city. They play an important role in retaining the identity of the built form of Beijing as a historical one. Furthermore, this study has also found that the public's attitude towards the demolition and the preservation is a function of social, cultural, economic, and political context of which the actions take place. This functional relationship is especially clear when studying the public's reactions to the preservation of courtyard houses and neighborhoods. The reactions vary from time to time of often changed social, economic and political context, and among people of distinctive cultural, social and economic background. Examination of the public's evaluations and preferences of the newly built environments constructed since the 1950s presents a mixed picture. On one hand, those of the neo-classical style which adopts traditional architectural vocabulary and thus are in harmony with the old built form are much more preferred and liked by the public than new buildings of modernistic style. The former are the public's favorite largely because they have elegant appearance of aesthetic quality and possess meanings associated with the traditional architectural style. But on the other hand, the public felt that adding modernistic high-rise buildings to the city has risen the level of modernization of the city, which is highly desirable and appreciated. To a large extent, modernistic high-rise buildings match the public's expectation of what modern Beijing should be.