Background and Objective: BMI is the most important international indexes for physical health assessment and it is a tool for awareness about optimal nutrition during adolescence. The Aim of this study was a survey about the impact of nutrition on BMI of guidance school and high school students of ghaemshahr city in the academic year 2010-2011.Methods: This study is the kind of applied studies that was performed with analytical descriptive, cross-sectional method. The samples of this research were obtained through the table of Kerjcie and Morgan and cluster random sampling method and between guidance and high school students of ghaemshahr city. The volume of samples was 305 people. The collected data were analyzed using SPSS software and associated tests.Results: 52.5% of samples were male and 47.5% were female, 57% of subjects were under weight, more than 13.8% was obese and very obese, and only 29.2% of the sample have normal weight. There was a significant difference between high BMI and consuming fried foods, the speed of eating, eating while watching TV or reading, difficult and low-calorie diet, oil consumption, the number of obese people in the family, and the level of family education. But there was no correlation Between BMI and eating sandwich, chips and snack, milk, fruit juice, salads and vegetables, consumption of protein, carbohydrate, and homemade food, type of diet, the number of persons in family and the occupation of parents.Conclusion: the result of this study revealed the positive effect of education Level of parents and awareness of families about nutrition and BMI. Therefore it is necessary to increase the awareness of families about the nutrition of students.