This study evaluated the effects of two treatments for adolescent bulimia nervosa (BN), family-based treatment (FBT-BN), and cognitive behavioral therapy (CBT-A), on both attitudinal and behavioural outcomes at end-of-treatment. These associations were examined specifically relative to motivation for change in obsessive-compulsive (OC) features of eating disorder (ED) symptoms. Adolescents (N = 110) were randomly assigned to FBT-BN or CBT-A and completed assessments of eating pathology and OC-ED behaviour. Across both treatments, greater motivation for change in OC-ED behaviour was associated with improved attitudinal features of ED at end-of-treatment. Motivation for change did not demonstrate a direct or interaction effect on BN behavioural outcomes. Results suggest that adolescents with BN who are more motivated to change OC-ED behaviours at the start of treatment, FBT-BN or CBT-A, are more likely to demonstrate improvements in cognitions, but not behaviours associated with EDs, at treatment conclusion.