Introduction and Objective. Provision of healthy and high-quality school meals is an important solution to improve children's health and well-being. Moreover, the meals provided at schools should not only meet dietary guidelines but also questions of sustainability. The aim of the study was to develop a new index to assess the quality of school meal menus, specifically their accordance with actual regulations, dietary guidelines and some sustainability goals. Materials and method. The School Meal Index-Lunch Evaluation (SMI-LE) is an originally created index to evaluate the quality of 5-day school menus. The general idea is to reflect the healthy and sustainability issues that should be present in school canteens according to WHO and EU recommendations. The index was tested in a real-life situation and fifty 5-day school menus available online from primary schools located in different regions of Poland, in rural and urban areas, were assessed with SMI-LE. Results. The median value of SMI-LE equaled 52 /140 points. Most of the analyzed menus (72%) were classified as 'Medium' quality according to SMI-LE. The menus classified as 'Low' were characterized by the lowest energy value, the lowest content of calcium, magnesium, iron, potassium, and folates, while the highest of sodium. Menus from the 'Good' category had the highest nutritional value, as well as the lowest sodium content. Conclusions. A novel tool to has been provided for measuring the quality of school meals that addresses health and sustainability issues. It responds to the need for new indices that would consider changes in dietary guidelines and increasing knowledge about the impact of food systems on the environment.