Introduction: one of the biological factors that is influential in teenagers' functions is circadian rhythms to which individuals have differences and certain preferences. The present research was carried out with the aim of comparing the five-factor model of personality in students with morningness and eveningness rhythms.
Method: The research methodology was descriptive-analytical. 100 pre-university students (50 with morningness rhythm and 50 with eveningness rhythm) in the 95-96 school year were selected with purposive sampling. Data collection tools were Morningness-Eveningness Questionnaire (MEQ) and NEO Five-Factor Inventory (NEO-FFI). Analysis of variance was used to analyze the data.
Results: There are significant differences between neuroticism, extroversion, openness to experience, agreeableness, and conscientiousness between morningness and eveningness groups (p<0/05). People with morningness rhythm have higher conscientiousness and agreeableness, while people with eveningness rhythm have higher neuroticism, extroversion, and openness to experience.
Conclusion: The results of the present research can be used for a more detailed planning to elicit students' maximum capability in useful hours of the day, as well as informing families to prepare the grounds for shaping adolescents' circadian rhythm in their sensitive development years.