Background: One of the ten most severe mental disorders is obsessive compulsive disorder (OCD). Psychiatric nurses play an important role in providing care to affected clients. Aim: this study explore the effect of metacognition appraisal and insight on the severity of obsessional beliefs among patients with obsessive compulsive disorder. Design: A descriptive correlational was used in the current study. Setting: The study was conducted in the out-patient clinics of Assiut university psychiatric hospital. Subjects: A purposive consecutive non-probability sample of 69 OCD patients. Tools: Demographic and clinical data questionnaire; Yale-Brown Obsessive Compulsive Scale (Y-BOCS); Metacognitions Questionnaire (MCQ-30); and Overvalued Ideas Scale (OVIS) were used to collect the data. Results: The patients' scores of the Y-BOCS, OVIS and MCQ-30 were significantly higher. There was a significant positive correlation between Y-BOCS severity and OVIS insight scores (r=0.459).The multivariate analysis showed that the OVIS score is the strongest independent positive predictor of the Y-BOCS severity score, while good family relations was a negative predictor. Regarding the MCQ-30, the control thoughts score was a positive predictor and the self-consciousness score was a negative predictor for it. Conclusion: Patients with OCD have more maladaptive metacognitive beliefs. Also, poor insight had negative impact on the severity of obsessive compulsive disorder. Recommendation: The effects of metacognition require further researches and designed educational program to improve patient's insight to reduce severity of obsessional beliefs.