This work was carried out to study the effect of using various types of junk food commonly used by primary and preparatory school students,and the biological evaluation on male rats Sprague Dawley Strain (70±10 g)the study continued for 45 days. Six groups of rats, each contains 5 rats, were fed on different tested diets Group (1): Control group rats were fed on basal diet. Group (2): rats were fed on basal diet supplemented with 10% of tomato flavor potato Chips. Group (3): rats were fed on basal diet supplemented with 10% of Doritos (sweet chili pepper). Group (4): rats were fed on basal diet supplemented with 10% of Windows (cheese flavor). Group (5): rats were fed on basal diet supplemented with 10% of Sunbites (cheese and herbs). Group (6): rats were fed on basal diet supplemented with 10% of Indomie (chicken curry flavor).Chemical, biological, biochemical and histological tests were carried out.The results indicated that ‎junk food contains high amount of fat and carbohydrates, and relatively low amount of protein and fibers. It also has a bad effect on kidney function, liver enzymes, immunoglobulin serum, brain enzymes, total antioxidant and lipid profile. However, there is an increase in the feed efficiency ratio (FER) and body weight gain (BWG) in all groups compared to the control group although the increase was not significant. It was concluded that junk food has a bad effect on health and may lead to a lot of diseases, especially for school students.We recommend that further studies should be done to find out the type of food additives.