The Development of Tendai Buddhism in Heian Japan in Tendaizasuki Pei-Chun Kuo (PhD Candidate, History Department of National Taiwan University) Tendaizasuki 天台座主記which provides chronological records of Tendaizasu, the leader of Japanese Tendai School, is an important source to realize the history of Japanese Tendai Buddhism. With Tendaizasuki, not only the personal background of Tendaizasu, but the incidents between them can be observed. Also, many daijoukancho太政官牒(official letter sent by the great council of state) and senmyo宣命(Emperor's order) were preserved, and became remarkable statement of the management of temples in Heian Japan. Along with the development of Tendai Buddhism in Japan, a proper management to control this huge organization was required. This article will focus on the management of temples, through the analysis of Tendaizasu and Betto別當, to illustrate the characteristic of Enryaku-ji延曆寺, and discuss the development of Tendai Buddhism in Heian Japan. Japanese system of rankings for Buddhist clergy has been developed in Nara period, with the transition of political background, it has been challenged by Tendai Buddhism in Heian period. By means of the accounts of early Tendaizasu, the significance of this position, and the contexts of its development will be clarified in this article.