This study was carried out to find the relationship between the eating disorder associated with BMI(body mass index) and nutrition knowledge by surveying 476 middle school girl students in Won Ju, Gang-Won Province, South Korea. BMI is a standard suggested for oriental people and it was differentiated into the underweight, the normal weight and the overweight. To determine the eating disorder, EAT-26(Eating Attitude Test-26) was used and in order to find out the level of nutrition knowledge DGE (Deutsche Gesellschaft fur Ernahrung) was used after some modifications and supplementations. And the results are as follows; 1) Out of the students surveyed, 22% are in underweight group, 64% are in normal weight group and just 12% are in overweight group. Except the students in underweight group, most of the surveyed students wish to lower the weight below normal weight. 2) Relationship was found between BMI and EAT-26 score that is related with eating disorder behavior, Total score was higher in overweight group than in underweight and normal weight group (P<0.001). When the score for individual question about eating disorder is considered in detail, the score for the questions preoccupied with the weight reduction was higher in overweight group than in underweight and normal weight group(P<0.001). For the questions about bulimia there was no difference according to BMI, however, for the questions about restraining food intake the score was high in overweight group(P<0.001). 3) The score of nutrition knowledge in line with BMI was different. It was found that the total score and the score for the questions about fat, calorie requirement, and calorie content in food were different. The total score showed the highest in overweight group in comparison with the ones in underweight and normal weight group. (P<0.05). Out of maccronutrient like carbohydrate, fat and protein, only the fat showed significant difference according to BMI and it was lower in overweight group than in underweight and normal weight group.(P<0.05) Out of the questions about calorie requirement, significant difference was found in the score for the questions about calorie requirement and calorie content in food. It was lower in overweight group than in underweight and normal weight group (p<0.05).