Background Posttraumatic stress symptoms (PTSSs) is known to be a typical problem for school bullying victims. However, the underlying mechanism between school bullying victimization and PTSSs remains unknown. This study examined the mediating roles of feelings of insecurity and self-disclosure in the relationship between school bullying victimization and PTSSs in adolescents. Methods Self-report questionnaires were used to assess 5013 adolescents; 443 of them with school bullying experiences were selected to carry out this study. Results The results found that school bullying victimization was directly related to more PTSSs, indirectly associated with more PTSSs through feelings of insecurity, and through the path from feelings of insecurity to self-disclosure. However, school bullying victimization did not exert an indirect effect on PTSSs through one step effect of self-disclosure. Conclusions These findings indicated that feelings of insecurity and self-disclosure mediated the relationship between school bullying victimization and PTSSs. The psychological service should reduce adolescents’ feelings of insecurity and give them more chances to disclose their bullying experiences.