Background: One of the most challenging issues in public health is childhood obesity in the 21st century. In Iran, the overall prevalence of overweight has increased and the total rate of obesity was estimated to be 12.3% (calculated as 6.5% for individuals less than 18 years). Objectives: The present study aimed at determining the diet knowledge and diet behavior among students in Shiraz, Iran. Methods: This cross-sectional study was conducted among 2040 students in 8 selected public high schools in 2013 in Shiraz, Iran. Random sampling method with proportionate allocation to size was used. To collect data, a standardized pretested questionnaire was used. The data were analyzed using SPSS.