This study investigated (1) the associations of homophobic bullying victimization in childhood with borderline personality disorder (BPD) symptoms in early adulthood among gay and bisexual men; (2) the mediating effect of depressive symptoms on the association between homophobic bullying victimization and BPD symptoms, and (3) the moderating effects of perceived family support on the association between homophobic bullying victimization and BPD symptoms. A total of 500 gay or bisexual men aged between 20 and 25 years were recruited into this study. The experiences of physical, verbal and social relationship bullying victimization during childhood were evaluated using the Mandarin Chinese version of the School Bullying Experience Questionnaire. The experiences of cyberbullying victimization during childhood were evaluated using the Cyberbullying Experiences Questionnaire. BPD symptoms were assessed using the Borderline Symptom List. Depressive symptoms were examined using the Center for Epidemiologic Studies Depression Scale. Perceived family support was evaluated using the Family Adaptation, Partnership, Growth, Affection, and Resolve index. The results of mediation analyses demonstrated that all the types of homophobic bullying victimization in childhood were directly associated with BDP symptoms in young adulthood as well as indirectly associated with BPD symptoms through the mediation of depressive symptoms. The results of moderation analyses demonstrated that the association between homophobic bullying victimization and BPD symptoms decreased when the individuals had more family support. Intervention programs to reduce homophobic bullying victimization and enhance family support for gay and bisexual men and their families are necessary. Interventions to improve depressive and BPD symptoms among gay and bisexual men are also necessary, especially for those who experienced homophobic bullying victimization during childhood.