Introduction and objective of critical thinking refers to individual’s ability to analyze and evaluate data. Such skill has become an inevitable necessity in social life more than life. Therefore, development of critical thinking skills is one of the most essential objectives of education on different levels from elementary school to higher education across the world, and individuals’ mental health is highly affected by the quality and the type of their thinking skills. On this basis, the present research studies the relation between mental health and critical thinking among students of educational science in the Islamic Azad University, central Tehran branch (Vali-e-Asr Complex). Sample size was 330 students, of which 180 students were selected by simple randomized method based on Morgan’s table, and the questionnaire was administered to them. Data collection was conducted by means of California critical thinking standard questionnaire, form B, and Goldberg’s general health questionnaire, 28-item form. This research was of correlation type, and research data were analyzed using indices of descriptive statistics and inferential statistics (Pearson’s correlation coefficient). The results of data analysis suggest that physical symptoms have a significant direct relation with overall score of critical thinking, and they don’t have a significant relation with its factors. Also, the results suggest that social dysfunction has a significant relation with analysis factor of deductive and inductive reasoning evaluation and overall score of critical thinking. Further, anxiety has no significant relation with any of the factors of critical thinking, and depression does not have a significant relationship with any factors of critical thinking. Given the relation between mental health and critical thinking, it can be concluded that raising critical thinking among students can raise the level of students' mental health, leading to mental health, especially considering that it is even more necessary for students of fields of studies related to education (psychology, educational sciences, counseling, etc.) to have critical thinking skills.