Urban development is one of the major issues that our country has always faced with in recent years. The formation of newly established areas alongside older neighborhoods in historical cities has created a specific typology for modern cities on the path to development. A large part of the identity of the old neighborhoods, as noted by Maurice Halbwachs, is composed of collective memories of the locals, while in newly established urban areas, these collective memories are essentially non-existent. According to the requirements of modern life, they will not exist. In this research, the process of formation of urban identity in the old Vahdat-e-Islami (Shapour) neighborhood has been studied and evaluated in comparison with the relatively new neighborhood of Tehran's Shahrak-e-Gharb with qualitative case study method and with interviewing tool from residents of those neighborhoods. The findings indicate that the neighborhood was not able to maintain its own structure and undergoes major changes, retains its identity through collective memories involved in specific places of the locals; But Shahrak-e-Gharb, due to the lack of common spaces and the lack of collective memory and the growth in the demands of modern life, and the lack of social communication between neighborhoods, have less mass memories and thus a weaker independent identity.