Modified cognitive-behavioral therapy (MCBT) has been demonstrated to reduce anxiety in youth with autism spectrum disorder (ASD). However, non-response rates are fairly high. Few studies have investigated factors associated with response. Intolerance of uncertainty (IU) is a treatment target for anxiety and worry in neurotypical populations and has been linked to anxiety and ASD. We sought to examine whether IU affects outcomes following MCBT in 43 children, ages 8-14 years, with ASD without intellectual disability. Consistent with prior data, there was a significant reduction in parent reported anxiety following MCBT. Higher levels of pre-intervention IU predicted higher anxiety and worry pre- and post-intervention. These findings suggest that targeting IU may improve outcomes following MCBT in youth with ASD and anxiety.