Insecure attachment and impairments in reflective functioning (RF) are thought to play a critical role in borderline personality disorder (BPD). In particular, the mentalization-based model argues that insecure attachment indirectly accounts for increased BPD features, notably via disruption of RF capacities. Although the mediation relationship between attachment, RF, and BPD is supported by previous evidence, it remains to be directly tested in adults with BPD. In the current study, a sample of 55 female adult BPD patients and 105 female healthy controls completed a battery of self-report measures to investigate the interplay between attachment, RF capacities, and BPD clinical status. Overall, the results showed that BPD patients pre- dominantly reported insecure attachment, characterized by negative internal working models of the self as unlovable and unimportant to others, and decreased RF abilities. Our findings further indicated that actual RF capacities mediated the relationships between adult insecure attachment and BPD clinical status.