Background and aims: Adolescent smartphone addiction has received increased attention in recent years, and peer relationship has been found to be a protective factor in adolescent smartphone. However, little is known about the mediating and moderating mechanisms underlying this relation. The aim of this study was to investigate (a) the mediating role of self-esteem in the association between student–student relationship and smartphone addiction, and (b) the moderating role of the need to belong in the indirect relationship between student–student relationship and adolescent smartphone addiction. Methods: This model was examined with 768 Chinese adolescents (mean age = 16.81 years, SD = 0.73); the participants completed measurements regarding student–student relationship, self-esteem, the need to belong, and smartphone addiction. Results: The correlation analyses indicated that student–student relationship was significantly negatively associated with adolescent smartphone addiction, and the need to belong was significantly positively associated with adolescent smartphone addiction. Mediation analyses revealed that self-esteem partially mediated the link between student-student relationship and adolescent smartphone addiction. Moderated mediation further indicated that the mediated path was weaker for adolescents with lower levels of the need to belong. Discussion and conclusion: High self-esteem could be a protective factor against smartphone addiction for adolescents with a strong need to belong as these students appeared to be at elevated risk of developing smartphone addiction.