Purpose: Using data from a randomized clinical trial evaluating cognitive behavioral therapy (CBT) for children with autism and co-occurring anxiety, this study examined the relationship between autism features and anxiety symptoms throughout CBT. Methods: Two multilevel mediation analyses were run which examined the mediating role of changes in anxiety for changes in two core features of autism, (a) repetitive and restrictive behaviors (RRBs) and (b) social communication/interaction impairments, between pre- and post-treatment. Results: Indirect effects between time and autism characteristics were significant for both models, indicating that as anxiety changes, so do RRBs and social communication/interaction as the outcomes respectively. Conclusion: Findings suggest a bidirectional relationship between anxiety and autism features. Implications of these findings are discussed.