Women with alcohol use disorders (AUD) experience high rates of co-occurring conditions, such as depression and posttraumatic stress disorder (PTSD), which can complicate treatment engagement and response. Therefore, identifying factors that underlie alcohol use, depression, and PTSD symptoms in women with AUD has important treatment implications. The current study investigated emotion regulation as one such underlying factor. We tested a model that examined the extent to which changes in emotion regulation during treatment predicted women’s depression and PTSD symptom severity at treatment completion and subsequent alcohol use following treatment. The study included 48 participants enrolled in a randomized controlled trial of interpersonal psychotherapy versus usual care for women with co-occurring alcohol dependence and major depression. Assessments were conducted at baseline, posttreatment (16 weeks), and follow-up (24 weeks). Descriptive statistics of baseline data revealed heightened levels of emotion dysregulation in this sample, which were related to fewer days abstinent from alcohol, more negative consequences from alcohol, and greater PTSD symptom severity. Women’s lower depressive symptoms at the end of treatment were found to mediate the relationship between improved emotion regulation during the treatment period and greater abstinence following treatment. Posttreatment PTSD symptoms, however, were not found to mediate that relationship. These results suggest that improvements in depressive symptoms during treatment are associated with emotion regulation at the end of treatment, which may contribute to greater abstinence from alcohol following treatment.