There are a high proportion of Dunhuang manuscripts having Symbol of Baoshou (包首) Titles, but few scholar know that what its origin and function is. By studying the format of ancient book titles, this paper points that this kind of symbol stem from Qikou (契口) on Bamboo slips. Qikou evolves into Symbol of Baoshou Titles, which have four types in scroll period, and ultimately develops into Yuwei (魚尾) in the booklet period. This research has methodological values about the study of the materiality of Chinese ancient books.
