Interpersonal difficulties and emotion regulation are the core characteristics of borderline personality disorders (BPD). However, how emotion regulation strategies contribute to the association between interpersonal problems and borderline personality symptomatology have not been highlighted within cognitive theory. The current study aims to examine the mediator role of cognitive emotion regulation strategies between interpersonal problems and borderline personality beliefs. The study consisted of 648 (381 women and 267 male) people from Turkey. In addition to Socio-Demographic Form, Cognitive Emotion Regulation Questionnaire (CERQ), Inventory of Interpersonal Problems Circumplex Scales (IIP-32), and Borderline Personality Belief Subscale (BPBS) were used to collect data from participants. Results showed that negative cognitive emotion regulation strategies, particularly catastrophizing, blaming-others and self-blame, mediated interpersonal problems, and borderline personality beliefs. Since the current study used thought-based assessment, the findings provide enlightening information to understand the underlying cognitive processes of the borderline personality pattern, and promising clinical implications to improve intervention programs within cognitive therapy approaches.