Many survivors of sexual violence disclose their experience to others. When they receive negative social reactions, this can be a traumatic event for the survivor where their trust towards others is violated and can cause posttraumatic cognitions and depression. Likewise, institutional betrayal, or negative reactions from trusted institutions regarding the disclosure of sexual victimization can be a traumatic event for the survivor and is associated with depression as well. However, studies investigating the mechanism underlying the relationship between institutional betrayal and depression is yet limited. Therefore, based on cognitive behavioral theory (CBT), which is known as the most effective approach to date for understanding and treating posttraumatic symptoms, this study examined if posttraumatic cognitions mediate the relationship between institutional betrayal and depression. Questionnaires were administered to 462 women who had experienced institutional betrayal to their sexual victimization. Results showed that institutional betrayal had an effect on depression only through negative cognitions about the self and world. This suggests the importance of identifying and treating trauma-related cognitions in order to prevent or cure depression of those who had experienced institutional betrayal to their sexual victimization. Limitations and implications of this study are also discussed.