In order to facilitate the information passing during the entire life cycle of products, ontology technology is introduced into the new generation of GPS. Ontology of size limits of the new generation of GPS is constructed by Protégé in this paper. This paper extracts main concepts of tolerance, fundamental and limit deviations and defines the correlations between the concepts. Protégé is used to establish treelike hierarchical structure and correlation of the concepts which are handled as classes in ontology. Some individuals are added to facilitate the reasoning and using of the ontology. SWRL rules are defined to reason and query relevant tolerance and deviation values. A query case of size φ25H7 which gives nominal size, fundamental deviation symbol and tolerance grade shows that the size limits ontology achieves the query of size limits values with given conditions.