The term lifestyle which comprises social, cultural, and economic elements has a profound impact on behavioral patterns and mental attitudes of individuals in the society and affects the architecture of their living place. In the recent decades, the discourse of housing choice pattern and living space in relation to lifestyle as a new subject has attracted the attention of the researchers and scholars in various fields of study including architecture and urbanism. One of the manifestations of the lifestyle is the quality of housing choice pattern as well as the quality of the living place which in turn exerts an influence on the architecture of the houses. The present study sets out to investigate the extent to which western lifestyle affected people’s lifestyle in the late Qajar dynasty in Hamadan and the influence that this kind of lifestyle had on the architecture of the houses in this period. The study employed a historical-interpretive analysis methodology.The data for the study were collected using library resources and field study. The samples for the field study were selected based on purposive sampling. In order to select the sample houses, all the documented houses which dated back to the late Qajar period and lent themselves to field study were examined. As many as six houses which displayed greater architectural developments due to lifestyle changes were selected. More specifically, the houses which were affected more profoundly by the western lifestyle in terms of architectural features in three macro-level, middle level, and micro-level were selected. The results showed that lifestyle changes occurred in social, cultural, and economic levels which in turn overshadowed the architecture of the houses, too. These changes were first demonstrated in the houses belonging to the grandees and merchants. The architectural evolution in these houses was examined at macro, middle, and micro levels. At the macro level, the simplicity of form and the elimination of multiple courtyards were significant. At the middle level, an evolution in the organization of the interior space and its development was observed. Finally, at the micro level, the symbolic significance of some architectural elements such as columns, stairs, and decoration was notable.