This study sought to look at the relationship between locus of control (LOC) orientation and academic achievement (ACH) of university-age English Foreign Language (EFL) learners. LOC is the extent to which individuals attribute their achievements either to external influences such as fate or to their own efforts. The sample for the study included 120 students studying English literature at the department of Foreign Languages and Linguistics of Shiraz University. They were chosen conveniently, on a voluntary basis, from the sophomores, juniors and seniors. The instrument used was the revised version of LOC questionnaire (Rotter, 2003) which identifies orientations of internality or externality. The participants' grade point averages were the measure of their ACH. A number of statistical analyses such as Pearson product-moment correlation, the regression analysis and the T-tests for the independent samples were performed on the data to achieve the objectives of the study. The findings of this study revealed that (a) the LOC and the socio-economic status (SES) have significant relationships with the university EFL students' ACH (b) the LOC is a good predictor of the participants' ACH (c) the internals perform at higher levels of achievement than the externals (d) there is a significant difference between mid/high SES-students and low SES-students in LOC orientation (e) the external students with a mid/high SES achieve significantly lower averages than the external students with a low SES, but the internal students with a mid/high SES achieve only a little lower averages than the internal students with a low SES (f) the internals' grades for the general and the major courses have significant relationships with their LOC, but this is not so for the externals (g) the age and the year of the study do not have significant relationships with LOC and with ACH (h) there is no main difference between male and female participants in LOC orientation (i) and finally, there is not a significant difference in the relationship between LOC and ACH due to gender. Thus, the teaching directors and the instructors should seek ways of enabling EFL learners to take control of their learning. (PsycINFO Database Record (c) 2016 APA, all rights reserved)