Introduction: The objective of the current investigation was to introduce the metacognitive model of obsession and to Explore the efficacy and effectiveness of this model in the treatment of ob- sessive compulsive disorder.

Method: In a single-subject experimental trial of multiple baseline type, the treatment process was carried out on a female subject. The subject was assessed at both pretreatment (baseline) and post treatment (eighth session) using Yale-Brown Obsessive Compulsive Scale (Y-BOCS), Depression Anxiety Stress Scale (DASS),  Subjective Unit Distress (SUD), Dysfunctional Attitude Scale (DAS), Thought Control Questionnaire (TCQ) and Self-Esteem Inventory (SEI). In addition, the first three scales were again completed by the subject at the first, fourth, and follow-up sessions.

Results: The score of the subject decreased from 38 at pre-intervention to eight at post-inter-vention in the Y-BOCS. There was also a reduction in her depression, anxiety, and stress. The sub- ject’s score decreased from nine at pre-intervention to three at post-intervention.

Conclusion: The treatment approach based on Wells’ metacognitive model was effective in the treatment of obsessive-compulsive disorder.