Introduction: Age and gender are among the variables related to individual differences that play an important role in self-knowledge, epistemological beliefs and personality traits. The aim of this study was to compare self-knowledge, epistemological beliefs and personality traits of students based on age and gender. Methods: The study method was descriptive-comparative. The statistical population of the present study included all students of universities (Azad, Payame Noor, Applied Science and Technology, Non-profit and other national universities) in Tehran in the academic year of 1996-97. 400 students were selected by cluster random sampling. The research instruments included a demographic questionnaire, the “ Integrative Self-Knowledge Scale” , the “ Epistemological Beliefs Questionnaire” , and the “ NEO Five-Factor Inventory” . The validity of the instruments was confirmed by face validity and reliability by internal consistency by calculating Cronbach's alpha coefficient. Data analysis was performed by SPSS. 23. Results: There was a significant mean difference in the scores of "agreeableness" personality traits in the group of male and female students and women scored higher than men (P <0. 05). Also, there was a significant mean difference in the scores of epistemological beliefs of "fast learning" (P=0. 001) and personality traits of "neuroticism" (P=0. 001), "agreeableness" (P=0. 022) was present in students in terms of calendar age. Students in age groups (18-29) learn faster more grades; and in neuroticism and "agreeableness", they got lower scores than the age groups (36-47) years. Younger students (18-29) believed in fast learning more than older ones (47-36), and had lower "neuroticism” and agreement. Conclusions: Female students had a more "agreeableness" personality trait than male students. Also, the younger the students, the more they not only believe in "fast learning" (epistemological beliefs), but also have a lower "neuroticism" personality trait; However, their degree of "agreeableness" is lower than that of students in higher age groups. Therefore, it is suggested that public health professionals, in examining students' selfknowledge, epistemological beliefs, and personality traits, also pay attention to their gender and age factors.