With the rapid growth of high-school food service in a short period as a result of the extensive implementation of school service, contract food service as well as the use of pre-prepared food ingredients has been increased. The purpose of this study was to evaluate the time required in various phases of product flow, temperature, pH, Aw, microbiological quality of foods served in high school in Seoul area and to analyze the hazardous factors to find out efficient control methods. Comparison was made between the schools using prepared food and raw materials in terms of microbiological quality. However, no distinguishable difference in the quality of foods was found between them. Therefore, the use of prepared food seemed no impose more hazard than using raw materials.