Scholars in higher education deem reflective thinking as integral to the development of professional disciplinary practices. One of the major issues in studying reflective thinking pivots around its conceptualization and assessment. Over the years, researchers have used several methods and scales to measure reflective thinking. One of the most widely known scales of reflective thinking was constructed and validated by Kember et al. (2000). It is entitled "Reflective Thinking Questionnaire (RTQ)" and includes 16 items measuring four types of reflective thinking: understanding (UND); reflection (REF); critical reflection (CREF); habitual action (HA). The present study aimed at validating the Persian version of RTQ among one hundred ninety-six English as a foreign language (EFL) university students. It then scrutinized the role of reflective thinking in academic achievements measured by grade point average (GPA). The association of learners' reflective thinking style with their educational level and gender was also estimated. To conduct the research, the scale was first translated into Persian and its validity (computed via confirmatory factor analysis, convergent, and divergent validity estimates) and reliability (computed via Cronbach's alpha) were substantiated. It was indicated that among the comprising factors of reflective thinking, UND received the highest mean followed by REF and CREF.