Objectives: Thought fusion is an important psychological construct of metacognitive model related to obsessive-compulsive disorder. In the present study the psychometric characteristics of “Thought Fusion Instrument” (TFI) was assessed in Students of Isfahan University. Method: After translating the original version, the final form of TFI was administered to 130 undergraduate students of Isfahan University. To examine the reliability of the TFI, methods of internal consistency (Cronbach’s alpha and split-half coefficient) were used, and validity was assessed using convergent validity, discrimination validity and factor analysis. Results: Internal consistency indicated the alpha coefficients to be 0.87, 0.77, 0.82, 0.80, and 0.73 for the total, first, second, and third factors and split-half coefficient respectively. Multivariate analysis of variance (MANOVA) for assessing diagnostic validity between the patient and the normal group indicated that the two groups have significant difference (p<0.001) regarding the total factor and its subsets. The correlation coefficient of TFI with Thought-Action Fusion was 0.65. The results of factor analysis using varimax rotation showed three factors: 1. Thought action fusion, 2. Thought object fusion, 3. Thought event fusion. Conclusion: TFI has satisfactory reliability and validity in Iranian sample and can be used for diagnosis and treatment.