Background: Today, the role of expert clinical nurses is highlighted because their presence is necessary for guaranteeing the quality of nursing care provided for the patients. However, there are no proper instruments for measuring the clinical competence of postgraduate students in intensive care nursing. Objectives: The present study aimed at development and psychometric evaluation of the clinical-competence inventory for postgraduate students of intensive care nursing. Patients and Methods: A methodological study was conducted at state nursing schools of Iran. The participants were postgraduate students of intensive care nursing, who were being trained at 16 nursing schools throughout Iran, during year 2014. After examining some relevant texts, the first draft of the inventory was designed with 60 items. In order to confirm its face and content validity, a panel of experts and students examined the inventory. The final draft, which contained 44 items, was distributed among postgraduate students of intensive care nursing, and 217 students answered the inventory. The construct validity was verified using exploratory factor analysis. The reliability of the inventory was verified using consistency tests. Results: Firstly an instrument with 60 items was developed. Next, the face and content validity of the instrument was assessed by 15 students and 11 experts. Overall, 16 items were removed through validity assessment and 44 items remained in the final draft. The content validity index of the final draft was 0.90. Moreover, the content validity ration of 44 items ranged between 0.75 and 1. The Cronbach’s alpha coefficient of the inventory was 0.95 and the intraclass correlation coefficient (ICC) of the test-retest results was 0.96. To examine the construct validity of the final draft, it was administered for 217 postgraduate students of intensive care nursing and five factors, with Eigenvalues above one and loading level equal to or above 0.4, were extracted through exploratory factor analysis. Conclusions: The inventory developed in this study is a suitable index for evaluating the efficacy of postgraduate students in the field of intensive care nursing.