The purpose of this study is to identify the guideline’s contents for dietitians’ knowledge, attitudes, and practices (KAP) for the sustainability management at school foodservice. The contents for the guideline were determined by the Delphi technique of two rounds. The Delphi panels of experts were consisted of sixteen school dietitians and fourteen professors of food and nutrition with more than 10 years of experiences by convenience sampling method. Based on the literature, knowledge, attitudes, and practices required for dieticians were classified into menu management, procurement, food production, facility and energy management, waste management, personnel management, and nutrition education. Data were analyzed using SPSS for Windows version 24 and EXCEL to calculate descriptive statistics, content validity ratio, degree of agreement, and degree of convergence. As a result of the second round, the validity scores of ‘knows eco-friendly certification standards and labeling systems (4.53 point)’ in the knowledge category, and ‘tries to purchase local agricultural products (4.87 point)’ in the attitude category were the highest. From that round in the practice category, the validity scores of ‘plan menus for students' health’, ‘purchases eco-friendly food’, and ‘conserves energy in pre-processing and cooking process’ were the highest with 4.73 point. Applying the criteria for securing the validity of the contents, the contents of 25 knowledge items, 20 attitude items and 30 practice items were confirmed. The findings of the study can be used to develop the guideline for dietitians required for the sustainability management.