Food composition data are detailed sets of information on food components, providing values for energy and nutrients, food classifiers and descriptors. The data of this kind is presented in food composition databases, which are a powerful source of knowledge. Food composition databases may differ in their structure between countries, which makes it difficult to connect them and preferably compare them in order to borrow missing values. In this paper, we present a method for mapping food composition data from various sources to a terminological resource-a food domain ontology. An existing ontology used for the mapping was extended and modeled to cover a larger portion of the food domain. The method was evaluated on two food composition databases: EuroFIR and USDA.