Throughout history, Iranian residential architecture has been formed based on a set of criteria that are implicitly aligned with the principles of sustainable development. In the meantime, social sustainability as one of the main pillars of sustainable development has played an essential role in spatial organization and social relations in traditional Iranian houses. However, in contemporary residential architecture, many of these factors have been toned down or eliminated. The purpose of this research is to identify the parameters of social sustainability in the design of residential houses in Tehran during the Qajar period and to investigate how they are reflected in the spatial and physical structure of these houses. The architecture of the Qajar era, especially after the era of Naser al-Din Shah, is considered a period of transition between tradition and modernity, where residential houses show a combination of traditional Iranian architectural patterns and western architectural influences. The present research method is analytical-applied and the studied samples include three Qajar houses of Dabir al-Molk, Motamen al-Atebba and Mehraban Menesh located in Naesri wall in 12 districts of Tehran. The results demonstrate that the parameters such as social justice, social interactions, spatial flexibility, maintaining privacy and social security, creating a sense of peace , ,connection between private and collective spaces, and taking advantage of the climatic components have played a decisive role in the social sustainability of Qajar houses. In the conclusion, based on the findings, suggestions for using these factors in contemporary housing design are provided.