This study reports the results of a study investigating the receptive vocabulary size of student EFL teachers. The study also examined the relationship between the participants' academic achievement (departmental GPA) and their receptive vocabulary size and the existence of any gender-related difference. The study was carried out in English Language Teaching (ELT) Department of a major state university in Turkey. A total of 104 undergraduate students (females: 76 and males: 28) enrolled in the department voluntarily participated in the study, took the Version 2 of the Vocabulary Levels Tests (Schmitt, Schmitt & Clapham, 2001) and responded to a survey investigating their GPA scores and genders. The results revealed that student EFL teachers have a high level of total receptive vocabulary capacity size in their foreign language (M=103.82). Learners' academic achievement (GPA) is treated as an indicator of their language proficiency level in many studies of English Language Teaching (ELT) field. However, the results of this study revealed that there was not any statistically significant correlation between academic achievement (GPA) and their receptive vocabulary size. Although GPA may be a sign of academic achievement (GPA) and successful studentship, it may not readily one's actual English language proficiency. The results also indicated that there was no significant difference between males and females regarding their receptive vocabulary size. (C) 2016 The Authors. Published by Elsevier Ltd.