This study was conducted to determine major factors underweight and obesity by comparing and analyzing dietary habits, exercise and weight control of obesity and underweight of Adolescents. The subjects were 26,039 students and they were divided according Body Mass Index(BMI). The collected data was analyzed through frequency, percentage, chi-square test. The results were as follows. 1) Among the male students 67.3%, 32.7% and among the female ones 82.7% and 17.3% were included in the underweight and the obese groups, respectively. 2) For dietary habits, the rate of skipping breakfast(12.5%, 13.6%) was considerably higher than those of skipping lunch and dinner. 3) The females and the obese group received more stress, felt more unhappiness, grief, depression and thought more suicide than the males and the underweight group, respectively. 4) The underweight group had higher rate of strengthening exercise of males and females. 5) For self-recognized body shape, while in the underweight group had a wrong image of their body shape, while more males in the obese group had a distorted self body image. 6) Measures to control weight were regular exercise, reduced amount of diet, and the obese group controled their weight more actively than the underweight group of the male and the female students. 7) From these results, appropriate mental health programs and education programs about health knowledge, properly self-recognized body shape and measures to control weight were considered to be necessary.