Objectives Several studies have reported an impairment of the mentalization capacity in borderline personality disorder (BPD). However, studies on the mentalization capacity in patients with BPD are scarce in Korea. The current study examined the clinical characteristics of BPD and its association with mentalization capacity. Methods Data from the study for developing a prospective clinical cohort and a Korean evidence-based treatment program for patients with BPD were analyzed. Fifty-nine participants (37 BPD patients, 22 healthy controls) were included in this study. The clinical characteristics, including depression and suicidality, adult attachment type, adverse childhood experiences, mentalization capacity, borderline personality symptom severity, resilience quotient, and temperament and character, were measured. An independent t-test, chi-square test, ranked ANCOVA, and multiple stepwise regression analysis were conducted for statistical analyses. Results Patients with BPD showed significant differences in mentalization capacity, adverse childhood experiences, attachment types, depression, and resilience profiles compared to the healthy control group. In this study, the impairment of mentalization capacity was significantly associated with temperament and character factors and borderline personality symptom severity. Conclusion The findings of this study suggest that mentalization capacity is associated with personality factors, including temperament and character, as well as the severity of personality psychopathology in Korean patients with BPD. Further analyses with a larger number of patients will be needed.