The present study examined the factor structure of the University of Tehran English Proficiency Test (UTEPT) that aims to examine test takers’ knowledge of grammar, vocabulary, and reading comprehension. A Structural Equation Modelling (SEM) approach was used to analyse the responses of participants (N= 850) to a 2010 version of the test. A higher-order model was postulated to test if the underlying factor structure, obtained in a data-driven manner, corresponds with the proposed structure of the test. The results revealed an appropriate model fit with the data, pointing to the fact that the three sections of UTEPT, i.e., structure, vocabulary, and reading, and their sub-components, except for the restatement section of reading, are good indicators of written language proficiency as assessed by the UTEPT. It was also found that the three sections assess distinctive constructs. The findings suggest that UTEPT is a valid measure of the written language proficiency of Ph.D. applicants to University of Tehran.