AbstractMaking errors is considered to be an integral part of language learning process. Therefore, it is of paramount importance that different types and sources of students’ errors be identified. The present study aimed to examine the types and sources of errors in a corpus of essays written by 40 Iranian university students. They were given a title and asked to write an essay having at least 150 words. Based on Keshavarz’s (2013) model for error analysis, the errors made by the students were identified and tabulated according to their frequency. Moreover, the errors were classified into intralingual and interlingual ones. The results of the study indicated that the participants made 404 different errors among them, 71.88% were caused by interlingual interference, and 23.84% of them were caused by intralingual factors. The results of the study can be informative for EFL teachers to be aware of the frequency and different types of learners’ errors in EFL writing classes and the reasons .....