The purpose of this study was to examine self-perception of body image and dieting behaviors by gender among high school students. The data were collected by a self-administered questionnaire during April, 2010, and analyzed by SPSS Windows V.18.0. The results were as follows. First, many respondents showed a desire to be underweight and regarded themselves as overweight, even though they had a normal BMI. Second, female respondents showed a higher level of concern about diet than male respondents. Third, male respondents received information about diet mostly from their family or friends, whereas female respondents received information from blogs, mini-homepages, or Kin-search on the Internet. Finally, female respondents showed a higher level of practice for fasting therapy than male respondents, whereas male respondents showed a higher level of practice for food therapy, drug therapy, oriental medicine therapy, and steam bath therapy. Therefore, high school should educate students to get right recognition and knowledge of diet.