Introduction: Intolerance of uncertainty (IU) is a transdiagnostic vulnerability factor characterized by a negative reaction at an emotional, cognitive, and behavioral level to uncertain situations. Aim: The current study investigates the factor structure, reliability, and convergent validity of the Iranian version of the intolerance of uncertainty scale-12 and its predictive role in anxiety, depression, and contrast avoidance (CA). Method: This is a cross-sectional, psychometric study. Two large samples (N1=1210, N2=228) were collected with the convenience sampling method from three university students in Zanjan city (i.e., University of Medical Sciences, Azad University, and Payame Noor University) who were studying from February to July 2020. Data were collected using CAQ-GE, BAI, BDI-II, GAD-7 and IUS-12. The data were analyzed with Mplus 7.4, Amos 24, and SPSS 26 software. Results: EFA and CFA supported the two-factor model for IUS-12. In addition, the results indicated that the IUS-12 has an excellent convergent validity (p<0.01) and an acceptable internal consistency (α=0.89). Regression analysis results confirmed the predictive role of IUS-12 in predicting anxiety and depression and pointed out the possible transdiagnostic nature of the CA. Conclusion: Iranian version of IUS-12 showed good psychometric properties and a robust two-factor structure. Therefore, using it in predicting constructs related to anxiety and depression could help us extend our knowledge of the underlying factors of psychiatric disorders.