Knowledge of cariogenic foods is a knowledge of foods that can cause dental caries. Practice to avoid dental caries is a practice taken to prevent dental caries. Knowledge is important in influencing one's actions. A good knowledge of health will have a tremendous impact on the way it acts so that it can have an impact in improving health. The purpose of this research is to know the description of knowledge and action to eat cariogenic food and caries number in the students of SDN Srondol Wetan 04 Kota Semarang.The type of this research is descriptive quantitative by using cross sectional approach. The sampling technique using purposive sampling with sample used as many as 57 students. The instruments used are questionnaires and OD sets. Data analysis in this study used cross tabulation.The result of this research showed that students have knowledge level about cariogenic food in medium category that is equal to 64,9% and action to prevent dental caries in medium category that is equal to 66,7% and caries student score in low criterion that is equal to 75,4%. It can be concluded that the level of knowledge and practices of students have a significant relationship in the incidence of caries suffered by children. It is advisable for students to maintain the diet and maintain dental health and the school to hold dental health education program about good food and bad for dental health so that can increase student knowledge.