Qumis is one of the most important areas in eastern Iran and along the Great Khorasan Road. Important sites have been surveyed, discovered and excavated in this area. In the meantime, many years have passed since archaeological excavations in the Tepe Hissar- Damghan. One of the buildings discovered in the Tepe Hissar is a building with a columned “Iwan” and a room with dome that are attributed to the Sasanian Period. Although there is no doubt about the history of building according to the Sasanian period, but according to some researchers, the building is a fire temple and according to the excavator and some others it is a palace. Considering that the characteristics of the palace and fire temple in the Sasanian period have been determined to a large extend by the studies that have been done, in this study we compare the known architectural elements and study historical texts and also refer to other researchers to answer questions, such as: What is the function of the building excavated on the Tepe Hessar? Palaces have a courtyard, Iwan and a room with dome in the public sector, and courtyards and rooms in the private sector; but in the fire temple all the architectural elements lead to the sacred place of the fire. For these reasons, and citing historical texts as well as the plan of building, it seems that we are dealing with a fire temple from the Sasanian period., although it shows similarities with plan of palaces of the late Sasanian period and early Islamic era.