Abstract: During the Kaiyuan and Tianbao reigns, Zhongshu Ling (the Chief Secretary of the Secretariat, ZSL) with exceptionally high political prestige enjoyed great favor and trust from the Emperor Xuanzong of Tang Dynasty and effectively acted as a prime minister in handling state affairs. After the An-Shi Rebellion (755-763), the newly established court of Emperor Suzong lacked individuals of sufficient prestige and status to appoint as ZSL. Consequently, state affairs were managed by Zhongshu Shilang (Vice Secretary of the Secretariat) granted the title of the prime minister. Therefore, the ZSL gradually marginalized in the court. Concurrently, distinguished ministers, like GUO Ziyi and LI Guangbi, were successively awarded the title of ZSL which then gradually became an honorary title. The adjustment of the ranks of the Zhongshu (Secretariat) and Menxia (Chancellery) headed by Emperor Daizong in the second year of Dali (767) completed the transformation of the ZSL’s role from a central to a peripheral position. The evolution of the ZSL’s authority from substantive to nominal during the transition from Emperor Xuanzong to Suzong and Daizong is demonstrated in the central court’s personnel arrangements following Emperor Suzong’s ascension. The evolution also results from continuous power struggles and adjustments of political system by the courts of Suzong and Daizong respectively.