During the Safavid period, Western culture infiltrated the traditional world of Iranians. The development of relations between Iran and France, changes in power structures, diverse tendencies, nationalistic and militaristic inclinations of Reza Shah, and so on, led to significant transformations in the social sphere of that era. These changes also influenced the architectural realm of homes. The aim of this research is to understand the physical structure of homes in Khorasan during the transitional period (late Qajar period and early Pahlavi period); this understanding focuses on the mass-space system. The main research question is: what are the architectural characteristics of Khorasan homes (from the perspective of the mass-space system) during the transitional period? This research is exploratory and has been conducted using both historical and descriptive-analytical methods. Data has been gathered through documentary and field methods. Among over 200 identified historical homes in Khorasan provinces, 35 significant homes in Mashhad, Firuzeh, Neyshabur, Sabzevar, Torbat-e Heydarieh, Boshrooyeh, Ferdows, and Birjand have been selected as exemplary samples. All samples belong to the late Qajar and early Pahlavi periods. The research results indicate that Khorasan homes during the transitional period had an inward-leaning tendency with low density, limited entrances, and indirect access to the house courtyard. Although the political, social, and cultural events of that era led to transformations in lifestyle, they did not have much impact on the architectural structure of homes in the eastern regions of the country. Perhaps the factors of religion and distance from the capital kept the architectural structure of homes immune to the deliberate societal changes that were taking place on a national level.