Due to the rapid growth of publications, librarians have been facing the problems caused by the shortage of stack as well as the quality deterioration of library collections. This naturally disappointed the user communities and the present library activities are weak and inadequate. It seems to the author that one of the desirable actions in remedying this problems is to weed library collections properly and regulraly. The purpose of this study is to establish weeding criteria in library collections, particulary in the fields of polictical science, economics and law In order to establish weeding criteria, shelf-time period which is the length of time that a book remains on the shelf between the last two users of a volume, was measured by examining the book cards or date-due slips of circulating books and collections which remained in the stack. The results of this study are as follows: (1) In the fields of political science economics and law, the shelf-time periods of general materials in Korean for circulation was measured. (2) This study shows shelf-time periods that vary in different subject fields. (3) Combining the shelf-time periods of books in active circulation and the total collection including books which have never been circulated, the size of library holdings which may satisfy a certain percentage of the current circulation can be estimated.