BACKGROUND Given the close relationship between life style and mental health and the importance of students as valuable human resources, the present study aimed at determining the relationship between life style and mental health among medical students in Kermanshah. METHODS This is a descriptive-correlational study that was conducted in 2018. The study involved 200 medical students. The sampling method was convenience sampling. Demographic questionnaire, general health questionnaire, and life style questionnaire were used for data collection. The data were analyzed Pearson's correlation test and regression analysis. The significance level was considered 0.05. RESULTS The mean mental health score of the students was 25.43 ± 13.02 (2 points higher than the cutoff point of this test). The life style of 59.5 students was moderate. The results showed that all life style subscales had a negative significant relationship with the total mental health score and all its subscales (P < 0.05). Among the life style subscales, the highest relationship and predictive power to mental health were obtained for psychological health, social health, sport and fitness, and environmental health (R 2 = 0.48, P < 0.001). CONCLUSIONS According to the results, the life style of most medical students in the final year of Kermanshah University of Medical Sciences was moderate. Further, the students had a better life style, and they had higher mental health. Therefore, considering the vital role of medical students in providing and promoting community health, the need for more detailed planning and interventions to improve their life style and mental health is essential.