A Comparative Study of the Syntactic & Morphological Errors of Iranian EFL Learners with Reference to Persian as Their First Language Since the term Error analysis was given unprecedented significance in the late sixties, as a reaction to CA, a number of studies in the field of second language learning have addressed this unusual phenomenon because of the wide ranging implications that this area of research has for explaining the nature of human language faculty and the process of language acquisition in general. Although over the years, each particular aspect of EA has been examined by different scholars, a lot more is needed to extract different kinds of errors and to analyze them scientifically. This research study was an attempt to examine the notion of error as a deciding area in the field of second language acquisition and the major causes for making errors across learners and analyzing their major syntactic problems categorizing the errors and estimating the frequency of each group of errors according to previous scientific measures. This study was particularly aimed at identifying the sources of syntactical errors of Iranian English learners and illustrating the role of mother tongue interference as the basic source of errors in this study. The performance data was gathered from a subject pool consisting of 250 learners from a more or less the same background learning English as their foreign language who attended TOLIMO, which is a test for Ph.D. applicants in Iran. In this study, different pattern of syntactic morphological errors, their frequency of occurrence and the overall shapes of error production curves were analyzed across a particular group of participants who attended TOLIMO Test to reflect the sources of their errors. Since the field of EA has a greater capacity for revealing the learners' system of errors, it is crucial to uncover this system in order to discover and explain the problems of ESL/EFL learners. A detailed study of the factors leading to errors would be a fruitful avenue to pursue for insights into the nature of learners' linguistic system providing us with clues to a deeper understanding of the acquisition process. So far, the aim has been to show how interference of mother tongue and intralingul effects are responsible for commitment of some syntactic errors in the writings of Iranian EFL learners. A lot more longitudinal studies will be needed to examine not only syntactic but orthographic, phonological, morphological and lexical errors of EFL/ESL learners.