Women are at notable risk for negative reactions from others following sexual victimization which serve to intensify negative posttraumatic outcomes. The current study tested the effectiveness of cognitive bias modification-appraisal (CBM-App) training targeting posttraumatic cognitions theorized to be impacted by positive and negative social support with forty-five female undergraduates, grouped by experiencing overall positive or negative post-assault support. Whereas all participants experienced improvements in posttraumatic cognitions at one-week follow-up, a crossover effect for intrusion symptoms was found; CBM-App training reduced intrusions in participants with negative support experiences yet increased intrusions in participants with positive support experiences. While findings highlight the need for careful selection of post-trauma interventions, the study is the first to integrate findings from CBM-App, sexual assault, and social support literature. Socially-relevant posttraumatic cognitions appear to be malleable and may be an important focus of treatment for survivors who experienced negative post-assault support.