Introduction: Generalized anxiety disorder is the most common anxiety disorder and has the highest rate of comorbidity with other psychiatric disorders. Excessive worry is the main diagnostic criteria for generalized anxiety disorder. The purpose of the present study is to examine the mediating role of meta-cognitive beliefs and cognitive emotion regulation deficit on the relationship between cognitive perfectionism and worry in generalized anxiety disorder.
 Materials and Methods: This is an exploratory-correlative study in which new correlations between variables will be examined. The statistical population includes patients suffering from generalized anxiety disorder referred to clinical centers in Tehran and Yazd in years 2012 and 2013. 100 consecutive referrals with generalized anxiety disorder (74 women, 26 men) were selected through purposeful sampling. All participants completed Perfectionism Cognitions Inventory (PCI), Penn State Worry Questionnaire (PSWQ), Meta-cognitive Beliefs Questionnaire (MCBQ), and Cognitive Emotion Regulation Questionnaire (CERQ). Data analysis was done through Pearson's correlation coefficients, two-steps regression analyses and SPSS software version 16.
 Results: Cognitive perfectionism as well as meta-cognitive beliefs and cognitive emotion regulation deficit had a positive relationship with worry in generalized anxiety disordered patients (P<0.001). Furthermore, data analysis revealed that the relationship between cognitive perfectionism and worry in patients with generalized anxiety disorder was mediated by meta-cognitive beliefs and cognitive emotion regulation deficit (P<0.001).
 Conclusion: It can be concluded that the relationship between cognitive perfectionism and worry in patients with generalized anxiety disorder is not a simple linear one. This is partly mediated by meta-cognitive beliefs and cognitive emotion regulation deficit.