Lifestyle which encompasses social, cultural, and economic factors deeply impacts upon the people's behavioral patterns and mental attitudes. One of the manifestations of lifestyle is the quality of selecting living places, which in turn influences the architecture of the houses.   The purpose of the present study is to examine the extent to which modern lifestyle affected Hamadanian people`s lifestyle as well as the architecture of their houses during the first Pahlavi regime. The study adopted a historical-interpretive analytical method which describes the modern lifestyle of Hamedanian people by taking the transition from tradition to modernity into account and investigates the conceptual components of the architectural modernism of the houses using architectural space analysis. The data for the study were collected through library resources and field study. The sampling method for the field study was purposive. To this end, all the houses built during the first Pahlavi regime which had documents and were possible to visit for a filed study were examined. The results provided evidence for the modernization of people`s lifestyle which led to  new concepts of modern lifestyle, such as consumerism, the development of social interaction, the initial formation of civility, social distinction and status, and social importance of women. Moreover, the findings show that changes in lifestyle resulted in the formation of three different architectural patterns. Garden houses, street houses, and evolved traditional houses were considered as reflections of architectural changes. These evolutions show the changes in people`s lifestyle   as a result of transition from tradition to modernity  and the evolution of architectural space due to the changes in the quality of modernism style of life.