Objective: To examine the mental health status of medical students with insomnia and to explore the characteristics of their personality and coping styles. Methods: Forty medical students meeting the criteria of CCMD-3 on insomnia and 53 normal controls were evaluated with Symptom Checklist 90 (SCL-90), Adolescent Self-Rating Life Events Check List (ASLECL), Coping Style Questionnaire (CSQ) and Eysenck Personality Questionnaire (EPQ). Results: Although life stressors between students suffering from insomnia and the control were alike, the former felt more stress in learning than the latter. The total mean score, certain factor scores (such as somatization, interpersonal sensitivity, depression, anxiety and psychoticism) of SCL-90, and three factor scores (such as self-accusation, fantasy and wince) of CSQ were higher in insomnia patients than in the control. There was significant difference in the stability of emotion between insomnia patients and the control. Conclusion: The level of mental health in insomnia patients who had more instable characteristics of emotion and lower tolerance for life events as stressors was lower than that of non-insomnia medical students.