This study aims to examine the effect of students' library after-school activities on the students and the school library from a marketing perspective and to recommend marketing strategies for school libraries. For the purpose, a questionnaire survey was conducted at nine middle schools in Seoul and Gyeonggi Province, and a series of statistical analyses with the survey data was performed in order for hypothesis testing. The results suggest that the effects of the school library marketing including customer loyalty were influenced by the student assistants' activities such as internal and experiential marketing factors. Furthermore, the activities of student library assistants can be linked to word-of-mouth marketing. Based on the results, ways to use student assistants in school library marketing are suggested.