Every generation occupies the city and its spaces in a different manner. Drawing upon its technical knowledge and the features of its period, each generation creates private and public spaces. Any intervention in the urban spaces requires a better understanding of the cities and their stories throughout the history. In late Qajar and early Pahlavi era, the developments in the West in some way paralleled the changes in urban design methods in the East. The prevalent method in the West was used in combination with traditional methods. Over time, such practices in the first Pahlavi era resulted in a historical disconnection between the local principles and methods of urban design. The purpose of the present research is to understand how the principles of urban design and its related fields have contributed to the formation of the squares during the first Pahlavi era. This research is interpretive and historical in nature.Data were collected through library research and field study. The samples of this research consisted of 28 squares formed in the first Pahlavi period (1921-1941) in the major cities of Iran. For this purpose, the key factors in the formation of new urban spaces in the first Pahlavi period were investigated. The factors included urban renewal, lifestyle, socio-cultural elements and technology; then the language of the urban design principles was developed based on Carmona’s urban design dimensions. The results showed that the design language was influenced by the factors contributing to the formation of urban spaces and reflected the changes in its creating factors. In fact, the differences in the changes occurred were unassociated with evolutions and prior historical changes and resulted in the urban spaces with a new design language which was different from the one used in a prior urban design. However, such differences were somehow reflected in the designs of the squares before the first Pahlavi era.