Introduction & Objective: Critical thinking is simply defined as ability for analysis and evaluation of information. Today, this skill is considered as an undeniable necessity for social life. So fostering critical thinking ability is one of the basic goals of different levels of education from primary school to higher education. Each conscious behavior is related to the theoretical and intellectual foundation and origin. Therefore, the quality and types of thought play an important role in human mental health. This research studies the relationship between female pre-university students' critical thinking skills and their mental health in the academic year 2009-2010 in Hamadan city.

Materials & Methods: This study is a cross sectional research and our method is based on correlation. Using random multiple stages clustering method, we selected 331 students as statistical sample. The data gathering instruments are two standard questionnaires: California form b critical thinking questionnaire and 28-question Goldberg and Hilier general health questionnaire. The data were analyzed using descriptive statistic indexes such as frequency, percent, mean and standard deviation and inferential tests such as Pearson correlation coefficient and multiple regressions.

Results: Research findings show that the average point of students' critical thinking skills is (6.51 out of 34) and their average point of mental health is (31.52 ).About 61 persons (18.4) percent have not any psychological disorder, about 270 person (81.6 percent) seemed to have psychological disorder symptoms. There are negative and significant differences between critical thinking skills and disorder in mental health. Multiple regression analysis show that: there is negative and significant differences between critical analysis and deductive rational skills with psychological disorder symptoms, that is when students' critical thinking skills increases, the psychological disorder symptoms decrease. Therefore the mental health status can be predicted according to students' critical analysis and deductive rational skills.

Conclusion: Research findings show that students' critical skills are weak and the majority of students are at risk of mental health: and when the level of critical thinking decreases, depression, anxiety, physical and social disorder symptoms increase. Therefore are educational and health managers recommended paying serious attention to these issues.