Objectives: This study analyzed the factors that influence the mental health of adolescents in Korea, China, and Japan. Methods: The survey was conducted in each country between November 2008 and January 2009. The respondents were 1,390 Korean, Chinese, and Japanese students aged between 14 years and 16. The mental health was measured by the School Mental Health Scale of Ochanomizu University (2004), which is composed of six scales: physical symptoms, eating disorders, depression, interpersonal relationship, powerlessness, and impulsiveness. Results: The relationship with family and friends are strongly associated with mental health. As for Korean and Chinese female students experienced mental illness more than male. Regarding Korean students, the time to use TV computer game is related to relationship and impulsiveness. The mobile phone use more than three hours is related to depression and relationship for Japanese, and the number of family member less than three, is associated with powerlessness for Chinese. Conclusion: Regular and effective health education is required in order to improve students lifestyles and family and peer relationships. This study also offers the fundamental information for health promotion programs for Korean, Chinese and Japanese students.