Background: Acceptance and commitment therapy (ACT) has been shown to promote willingness to experience intrusive thoughts among individuals with obsessive-compulsive disorder (OCD). Exposure with response prevention (ERP) delivered from an ACT framework (i.e., ACT+ERP) may facilitate changes in how patients relate to their unwanted internal experiences. Aims: Accordingly, the present study aimed to examine the effect of ACT+ERP on appraisals of intrusive thoughts, relative to standard ERP. Methods: Forty-eight adults who received 16 treatment sessions as part of a randomized controlled trial comparing standard ERP to ACT+ERP completed the Interpretation of Intrusions Inventory (III) at pre-treatment, post-treatment, and follow-up. Results: Results showed a significant main effect of time for all III subscales, suggesting that appraisals of intrusive thoughts shift over the course of treatment. The effect of the condition × time interaction, however, differed between the III subscales. Specifically, a significant interaction emerged for the control of thoughts subscale, such that individuals who received ACT+ERP experienced greater reductions in beliefs about the need to control thoughts. The interaction term was not significant for importance of thoughts or responsibility subscales. Conclusions: Findings suggest that augmenting ERP with ACT enhances change in beliefs about the need to control thoughts, but not in beliefs about responsibility and the importance of thoughts. Clinical implications and future research directions will be discussed.