The purpose of this study was to propose the improvements for high quality of National Library of Korea (NLK) Subject Headings List which was developed as a subject access tool in 2002. For this study, literature review, case study for subject headings lists of national libraries, and data analysis of headings and relationships were performed. Several problems were found as follows: inconsistency of subject headings descriptions, unclear and unnecessary relationships among headings, inconsistency of hierarchical relationships, lack of currency, incorrectness of classification numbers, duplication of newly requested terms, and assignment of non-preferred and unregistered terms in bibliographic records. Focusing on these problems, modifications of subject headings and bibliographic records, installation and operation of an review committee on subject headings, and supplementation of a manual were suggested to improve NLK Subject Headings List.