Purpose: The purpose of this study was to investigate the mediating effect of adult attachment in the relationship between eating psychopathology and depression among patients with eating disorders. Methods: Patients (N=146) who visited a clinic for eating disorders participated in the study. Data were collected from December 2017 to February 2018 using the Eating Disorder Inventory (EDI-2), Revised Adult Attachment Scale (RAAS), and Beck Depression Inventory (BDI-II). Results: The subjects showed high scores on eating psychopathology (drive for thinness 15.02±5.11, bulimia 11.77±5.27, and body dissatisfaction 14.16±7.82), adult attachment (attachment avoidance 37.31±6.18 and attachment anxiety 16.63±5.38), and depression (24.26±10.81), and 65.1% of the participants showed above a moderate level of depression. There were significant correlations among eating psychopathology, adult attachment, and depression. We also found that adult attachment fully mediated the association between eating psychopathology and depression. Conclusion: Future interventions for patients with eating disorders who have experienced insecure attachment with their primary caregiver should focus on forming a therapeutic relationship with the therapist. In addition, family therapy might contribute to lowering attachment insecurities and depression by recovering the attachment between the patients and their parents.