As a valuable part of Iran, Khorasan has made a significant contribution to the architectural history of this ancient land, and due to its geographical extent and historical background, it deserves to be studied and mosques have always been considered among the most significant buildings, The research method is descriptive-analytical and historical, and the statistical population of the research is the historical mosques of Khorasan, the sample size includes all the mosques registered in Khorasan from the beginning of Islam to the end of the second Pahlavi era, totaling 167 mosques. For this purpose, documents were first collected with the help of library sources, but due to the incompleteness of the documents, as well as some of them being illegible and unintelligible, as well as the presence and perception of the mosques closely, which is effective in knowing them from many sides, all the historical mosques of Khorasan were visited. From this number, some mosques were removed due to serious destruction and lack of knowledge of their shape and form, and some others were removed due to being in a complex of architectural buildings. Therefore, in the following, the collected data of 139 mosques were classified based on how the spaces are organized and how they coexist with each other, and then analyzed based on the type of spaces and the quality of the enclosure of the spaces used. Finally, based on the obtained information, the typology was done and the conclusion was made. The results obtained from the study of the architectural spatial structure of the historical mosques of Khorasan with the components of spatial enclosure, spatial elements and spatial organization, indicate that the historical mosques of Khorasan can be divided into five types based on the variety of spatial enclosure, each type according to the use of different types Spatial elements have their own subspecies to achieve it, and each subspecies based on the type of arrangement of spaces includes various organizational patterns. These types include: "closed", "closed and open", "closed and semi-open", "open and semi-open" and finally "closed, open and semi-open".