The aim of this study was to investigate the relationship among body image perceptions, a desire for thinness, and dieting behavior in young females in Japan. The subjects were 302 Japanese female university students (age 19.9 ± 1.4 years). An anonymous, self-administered questionnaire survey was conducted between July and August 2011. The questionnaire clarified the subjects’ physical status, perception about personal body shape, desired body shape, the time frame when they first thought about body shape dieting, exercise habits, and eating behaviors. The results revealed that many of the underweight or normal weight subjects perceived themselves as obese, and often the reasons for the perception of obesity were comparisons with others or with themselves in the past. The scores of EAT-26 in those who perceived themselves as obese were higher than the scores in those who did not. Those who perceived themselves as obese had a desire to become slim, were concerned about body shape at an early age, were concerned about dieting, had dieting experience, and were willing to increase daily exercise. These results indicated that incorrect perceptions about body shape have connection to a desire for thinness and dieting behavior.