Objective This study examined the mediating effects of experiential avoidance and interpersonal problems on the relationship between social anxiety and social networking service (SNS) addiction proneness. Methods An online survey was conducted on 400 university students in their 20s across Republic of Korea. The scales used in the study were the Social Interaction Anxiety Scale (SIAS), Korean Acceptance-Action Questionnaire-II (K-AAQ-II), Short form of the Korean Inventory of Interpersonal Problems Circumplex Scale (KIIP-SC), and SNS addiction proneness scale for university students. For data analysis, structural equation modeling was conducted, and phantom variables were used to verify the significance of individual indirect effects of the multiple mediation model. Results Social anxiety had no direct effect on SNS addiction proneness. Experiential avoidance and interpersonal problems completely mediate the relationship between social anxiety and SNS addiction proneness sequentially. Conclusion Our result suggests that experiential avoidance leads to interpersonal problems and SNS addiction proneness. In other words, it is important to alleviate experiential avoidance in treating or preventing interpersonal problems and SNS addiction proneness among university students with social anxiety.