This study was carried out to evaluate the associations between lifestyles and Body Mass Index in a group of 349 male and 65 female medical students, ages 17 to 31 years. 20.0% of male students and 3.1% of female students showed the over weight in the classification of obesity by Japan Society for Study of Obesity. There was no statistically significance in the comparison of the height, body weight, body mass index, obesity index and body fat(%) according to grade in both sexes. But male students showed increasing tendency of waist-hip ratio with grade. According to obesity category, there was significant difference in the comparison of body weight, body mass index, obesity index, waist-hip ratio and body fat(%), but height. Body mass index was positively related with waist-hip ratio(r=0.6150, p=0.0001) and fat(%)(r=0.5101, p=0.0001) in males and waist-hip ratio (r=0.4734, p=0.001) and fat(%)(r=0.4522, p=0.002) in females. This study provides an opportunity to further examine the relationship of sociddemographic factors and health behaviors to obesity, and suggest the basic concept to match the obesity study to general epidemiological cohort studies for controlling of chronic adult diseases.