This paper aims to propose ways to promote SNS marketing at school library sites with case study analyses in school libraries. To this end, in-depth interview was conducted with 10 Teacher Librarians who had used SNS in library operation and an in analysis was made of the operation status, motives and objectives, strategies and performances of the school library's SNS marketing. According to the study, most Teacher Librarians were found to be using SNS such as Facebook, Instagram, Kakao Plus Friends and so on in an attempt to improve accessibility and utilization of the library resources first. Not only that, they used SNS for the purpose of communicating with users while increasing the number of visitors and identifying the needs of users. The messages provided through SNS are information on school libraries and their reading programs, and the target market mainly involved their students. Based on the above research results, measures to promote SNS in school libraries were discussed, including the need for marketing consultative bodies, expansion of SNS targets, and enhancement of expertise in SNS.