The core features of borderline personality disorder (BPD) include problematic interpersonal relationships, behavioral and affective dysregulation, identity problems, and cognitive dysregulation. Cognitive dysregulation, such as catastrophizing, rumination, and thought suppression, contributes to emotion dysregulation in BPD. Previous research suggested that thought suppression fully mediated the relationship between negative affect intensity/reactivity and BPD symptoms. We predicted that catastrophizing similarly will serve as a mediator between negative affect intensity/reactivity and BPD symptoms. Two samples completed the study. First, students (N = 191) self-selected to participate in an online study through the university psychology research recruitment system. Additionally, a second sample using Amazon Mechanical Turk (MTurk; N = 172) was utilized. Catastrophizing partially mediated the relationship between negative affect intensity/reactivity and BPD symptoms.Across these samples, results suggest that catastrophizing may have a significant role in understanding BPD symptoms, which is similar with rumination.Limitations and future directions are also discussed.