This study examined change in defensive functioning during group psychodynamic interpersonal psychotherapy (GPIP) for women with Binge Eating Disorder (BED). Women with BED (N = 102) received 16-weeks of GPIP. Participants were assigned to a high or low attachment anxiety condition based on pre-treatment attachment anxiety scores. Three group therapy sessions (sessions 3, 8, and 16) from each of 12 groups were video recorded, transcribed, and participants were rated on an observer rating scale of defensive functioning, the Defense Mechanism Rating Scale. Defensive functioning was reliably assessed in this group therapy context and improved significantly during treatment. Change in defensive functioning was significantly associated with better self-esteem and lower interpersonal problems but only for women with high attachment anxiety. GPIP to improved defensive functioning, and change in defensive functioning for women with BED and high attachment anxiety is an important aspect for improving their self esteem and interpersonal problems.