This study was designed to investigate the amount of the expression of critical thinking (CT) and the nature of L2 in tasks that require critical thinking in English for academic purposes (EAP) classrooms in Turkish universities. This study was conducted with two advanced-level EAP classes, including 34 students in total, at Middle East Technical University, Turkey. The data was collected by video-taping the students’ discussion in class and analyzing their transcripts in terms of critical thinking and nature of language. The results indicated that students can express their critical thinking skills orally in L2 to a certain extent but they have difficulty in doing so as a result of their lack of necessary language. This study suggests the need for further work on oral expression of CT in EAP classrooms in Turkish universities in terms of the vocabulary and grammar students need to express themselves more accurately while engaged in tasks that invite CT in their oral L2.