The purpose of this study was to investigate nutrient intake and food behavior according to the nutrition knowledge of middle school students residing in Seoul and Kyunggi-do, Korea. Anthropometric measurements and questionnaires, including 24-hr recall of dietary intake, were collected from 543 male and female middle school students. They were assigned to one of five groups according to their nutrition knowledge : very high group (VHG ; 90 - 100 score), high group (HG ; 80 - 90 score), normal group (NG ; 70 - 80 score), low group (LG ; 60 - 70 score) and very low group (VLG ; < 60 score), and comparisons were made. The mean age of the subjects was 13.7 years old. The mean height, weight, and BMI of male and female students were 161.9 cm, 52.6 kg and 20.2 kg/$m^2$, 157.0 cm, 50.4 kg, and 20.4 kg/$m^2$ respectively. Female students skip breakfast and dinner more frequently than male students do. Male students skipp lunch and eat fast foods more frequently than females do. Protein, calcium, vitamin B$_1$, vitamin B$_2$, niacin, vitamin C, fat, and animal protein intakes in females are shown to be related to their nutrition knowledge. Calcium, protein, animal protein, vitamin B$_2$and niacin intakes are significantly lower in the VLG than in the others. However, vitamin B$_1$and vitamin C intakes are significantly lower both in VHG and VLG. Fat intake in VHG is lowest. Nutrition knowledge of male students is correlated with mothers knowledge, nutrition attitude and nutritional status. On the other hand, in female students, nutrient consumption was lowest in subjects whose nutrition knowledge was highest and lowest. Therefore, nutrient consumption is affected by nutrition knowledge. However, in female students, possibly due to wrong information on diet or prejudice and outlook, nutrient consumption was low even when they scored high in nutrition knowledge. In conclusion, nutrition knowledge of male students is affected by the mothers nutritional knowledge and attitude. Therefore, nutrition education for mothers is very important. In male students, as their nutrition knowledge is low, their nutrient consumption is affect. These results indicate nutrition education and correct information for body image, balanced diet, regularity of meals and food selection for middle school students are required at both school and home.