This study aims to determine the effects of mental health on obesity among Korean adolescents. The data in this study were obtained from the 2013 Korean Youth Health Risk Behavior Web-based Survey conducted in 70,354 adolescents aged twelve to eighteen (35,575 males and 34,779 females) from June 1 to 30, 2013. The variables included age, the economic status of household, academic achievement, health status, perceived happiness, perceived stress, satisfaction of sleeping, perceived depression, and suicidal ideation and the data were processed using t-test, chi square test, and logistic regression analysis. The general characteristics affecting obesity for both Korean male and female adolescents included age (p<0.001), the economic status of households (p<0.001), academic achievement (p<0.001), and health status (p<0.001); the variable of mental health affecting obesity was suicidal ideation among females (p<0.05). It is expected that female adolescents' experience of suicidal ideation can be used as information to predict the likelihood of obesity in managing an obesity program for adolescents and it is necessary to provide obesity education suitable for age and to include obesity guidance in consideration of gender and the economic status.