Objectives: This study was performed to determine the mental health of high school students, and specifically that of children with no siblings in urban areas, and we aimed at revealing the various potential influences of different psycho-social factors Methods: The participants were, 514 high school students who were the 1st- to 3rd-graders in Daejon City; they were, given self-administered questionnaires that required no signature during the period of March through June 2005. The analyzed items included the general character of the subjects, the symptoms of stress and depression for mental health, self-esteem as a psychological component, anxiety, dependent behavioral traits and, social support of family members and friends. Results: The study results suggested that the group of urban high school children with no siblings had a higher tendency for stress and depression than did the urban high school children with siblings. The mental health and psychosocial factors were found to be influenced by friends, a sense of satisfaction at school and home life, and emotional support as well. Conclusions: In conclusion, emotional support by the family members can improve mental health by reducing anxiety, stress and depression.