A study of the changes in different buildings and structures of the Islamic era indicates that the architectural changes in these buildings have, in a way, followed the traditions of previous eras. In fact, it can be said that the influence of Islamic culture in different times is one of the reasons for the continuation of such traditions. Moreover, in each period it has been tried to update and benefit from the models of the previous era based on the needs of society. Sepahdari School is one of the important buildings in the historical texture of Arak and the oldest school in the city dating back to the Qajar period. The present study aims to examine the architecture of this important building based on a descriptive-analytic method and some library and field studies. The conducted analyses demonstrate that the physical and architectural structure of Sepahdari School follows the construction method of four-iwan schools. They also reveal that this school was constructed following the method used in the building of previous schools in terms of its physical elements, geometrical designs, and several other techniques. Similar to many other schools, Sepahdari School is located on the way leading to the Bazar of the city and its economic and social center.