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.