Bakground. Caregiving is a strong source of stress and leads the family caregiver to experience the burden of being responsible for the care of a severely mentally ill family member. The Burden Assessment Scale (BAS) assesses burden in family caregivers. This study aimed to analyze the psychometric properties of the BAS in a sample of family caregivers of people diagnosed with Borderline Personality Disorder (BPD). Methods. Participants were 233 Spanish family caregivers (157 women and 76 men aged between 16-76 years old, M = 54.44, SD = 10.09) of people diagnosed with BPD. The BAS, the Multicultural Quality of Life Index, and the Depression Anxiety Stress Scale-21 were used. Results. An exploratory analysis resulted in a three-factor 16-item model (Disrupted Activities; Personal and Social Dysfunction; Worry, Guilt, and Being Overwhelmed) with an excellent fit (χ²(101) = 56.873, p = 1.000, CFI = 1.000, TLI = 1.000, RMSEA = .000, SRMR = .060), good internal consistency (ω = .93), a negative correlation with quality of life, and a positive correlation with anxiety, depression, and stress. Conclusion. The model obtained for the BAS is a valid, reliable, and useful tool for assessing burden in family caregivers of relatives diagnosed with BPD.