The major purpose of this paper is to examine the foundation date of Goseon-sa Buddhist temple and how the entire layout of the temple changed over time. The ruined temple site located in the eastern outskirts of Gyeongju is now submerged due to the construction of Deokdong-dam in the late 1970s. Since an archaeological excavation was conducted before the dam project, some information concerning the temple is available. It should be noted that the three storied stupa was moved to the Gyeongju National Museum. There is no direct historical document and material evidence concerning the foundation date of the temple. According to the Samguk yusa, however, it is certain that the temple existed in the second-half of the seventh century A.D. In particular, the historical record mentions that Wonhyo, one of the most famous Buddhist monks in Silla history, stayed at the temple. Since Wonhyo was born in 617 and entered Nirvana in 686, we can assume the existence of the temple. Gameun-sa Buddhist temple, located near the temple, is known to be constructed in 682. This indicates that Gameun-sa temple and Goseon-sa temple coexisted. It is of interest to note that there are huge similarities between the two temples in terms of the stupa style. On the one hand, this indicates the contemporaneity of the two temple, on the other hand by stupa alone, it is hard to determine which temple was constructed first. In order to examine the relative chronologies of the two temples, I examined two-stage circular pillar square cornerstones recovered from the different temples in Gyeongju. It is generally accepted that cornerstones for buildings during the unified Silla period are a good time marker. On the basis of the analysis of cornerstone styles, I came to a conclusion that Goseon-sa Temple may have been founded earlier than Gameun-sa temple. According to the outcome of the archaeological excavation, the entire layout of Goseon-sa temple changed over time. One of the most important things to be mentioned is that when Golden Hall of the temple was being constructed, the stupa was not being built at the same time. That is, the stupa was built later time period than the Golden Hall. At present time, it is hard to know why there was a time difference between the two main Buddhist architectures. It is worth while to examine the question in the near future.