This study aims to determine pre-service teachers’ cognitive structures and conceptual definitions for the concept of critical thinking, thereby revealing their perceptions about it. Document analysis, one of the qualitative research approaches, was employed in the study. The study group consists of 161 pre-service teachers from different departmental programs of a state university in Turkey (primary school teaching, mathematics education, science education, Turkish education, social sciences education and psychological counseling and guidance education) enrolled in the ‘Critical and Analytical Thinking’ elective course in the fall and spring semesters of the 2021–2022 academic year. A form consisting of open-ended questions prepared by the researchers was used as a data collection tool. The first part of the form consists of a word association test used to reveal pre-service teachers’ cognitive structures about critical thinking and the relations between the concepts in this structure while the second part involves an open-ended question in response to which they can write their original definitions for critical thinking. Content analysis method was used to analyze the data obtained from the form. The analysis showed that the pre-service teachers had rich cognitive structures for the definition and content of critical thinking, that they preferred to describe the concept of critical thinking as skill-based in their definitions and did not include critical thinking dispositions in their definitions as much as skills, although they emphasized many critical thinking dispositions in the word association test, that their definitions were consistent with the definitions in the literature, and that their perceptions of critical thinking were relevant to the nature of critical thinking.