This has been designed for an attempt to survey a library use competency in order to provide basic information to plan more effective library use instruction for high school students. To get necessary data, a questionnaire was sent to 450 students in the 7 sample high schools in Seoul, and $80\%$ of them responded. The followings are the analysed results. 1. $42\%$ of them responded that they have heard about the decimal classification and $15\%$ of all the students have ever used decimal classification to search for the materials. 2. $3.6\%$ responded that they can understand the decimal classification and $66\%$ of all the students want to know about decimal classification. 3. $94\%$ responded that they have heard about the catalog cards and $41\%$ of all the students used catalog cards to search for the materials. 4. $29\%$ responded that they can understand the catalog cards and $68\%$ of all the students want to know about the catalog cards. 5. $61\%$ responded that they can use reference books. 6. $55.6\%$ responded that they know about the parts of a book. 7. $11\%$ responded that they can footnote. Reviewing the results of this study, library use competency of high school students can be said to be below level. And more effective approach is expected.