The period between the First and Second World Wars brought structural changes to Iranian society. The First Pahlavi state (1925-1941) began social projects to transform traditional Iranian society into a modern westernized one. On the one hand, the establishment of a powerful central government, development of the state bureaucracy, nationalization of the education system, and state-sponsored industrialization produced a modern middle class, which could follow the desired Western lifestyle. On the other hand, the state systematically attempted to transform the traditional lifestyle of the other social groups by banning their social practices and regulating their spaces. This paper focuses on the spatial transformations of Tehran during the period between the two World Wars. It shows that the transformation of the city should be examined through the framework of the conflict between the modern and traditional middle classes. By examining social lives of the traditional and modern middle classes and their social spaces, this paper demonstrates how the policies of the state promoted one and abolished the other. Through the discourse analysis of Iranian periodicals and municipality’s regulations of the era, the paper argues that spatial policies of the state were effective tools for the transformation of Iranian society. In another word, the codification of spaces was a means of subjectification; the state was able to (re)produce its desired subjects through the subtle control of spaces. In this process, the modern middle class played a decisive role in the production of a power relation in which the traditional strata and their social spaces were depicted as backward, obsolete, traditional, religious, unhealthy, and sad and the modern middle class as progressive, European, secular, healthy, scientific, and happy. This paper argues that the First Pahlavi state utilized the social power of space as an instrument for social control and change, and the transformation of Tehran should be examined through this framework of the instrumental use of spaces and the conflict between the modern and traditional classes.