OBJECTIVE: Anxiety sensitivity (AS), the trait-like fear of symptoms of anxiety, has been associated with eating disorder (ED) pathology broadly, bulimia nervosa (BN) symptoms specifically, and the anxiety disorders that are commonly comorbid with BN. AS, especially for physical symptoms specifically, maybe a risk and maintenance factor for BN and comorbid anxiety. METHOD: Adult participants with BN (n = 44) in a clinical trial comparing CBT to mindfulness and acceptance-based treatment (MABT) reported ED symptoms, trait anxiety, and AS through treatment and follow-up. We predicted that greater early reduction (i.e., within the first month of treatment) in AS would predict greater reductions in ED symptoms and trait anxiety at post-treatment and follow-up. RESULTS: Early reductions in AS for physical concerns predicted lower ED symptoms and trait anxiety at post-treatment but not follow-up. Exploratory analyses indicated that treatment groups did not differ in either early or total change in AS, controlling for baseline AS. DISCUSSION: Early reductions in AS may be an important treatment target for BN, and may additionally support reductions in anxiety. Future research should identify which components of CBT and MABT best target AS, to deliver these components early in treatment, when they can have maximum effect. PUBLIC SIGNIFICANCE: Anxiety sensitivity, the fear of symptoms of anxiety, is associated with eating disorders (ED). In this study, participants in treatment for bulimia nervosa reported ED symptoms, trait anxiety, and anxiety sensitivity through treatment and follow-up. Greater early reductions in anxiety sensitivity predicted lower ED symptoms and trait anxiety at post-treatment. Future research should identify which elements of treatment best target anxiety sensitivity, to deliver them early in treatment.