Customization is a very important feature of any manufacturing scheduling system. In many cases large commercial manufacturing scheduling systems are not easily and efficiently customizable to meet requirements of small and medium size enterprises. Therefore, this paper proposes an ontology-based architectural solution for the customization of manufacturing scheduling systems. According to the approach, the input to the scheduling system is a customized manufacturing scheduling ontology that is an extension of the manufacturing scheduling ontology provided in this paper. The customized manufacturing scheduling ontology performs as a knowledge base and data access point for the manufacturing scheduling system and enables it to be easily adapted to different products and their manufacturing processes.