Turkish National Healthcare Information System aims to provide the interoperability between data at the distributed health systems. For the interoperability between the distributed health information systems, National Health Data Dictionary (NHDD) is used as a reference to all health institution in Turkey and it provides great contribution in terms of the terminology. For to be easily understandable and readable of NHDD by both humans and their applications in the web environment, definition requirements of NHDD occur as semantic. The core of the Semantic Web is ontology, which is used to explicitly represent our conceptualizations. Ontologies plays an important roles in health applications. In this study; we have developed ontology based NHDD using Semantic Web technology and proposed a methodology for the enrichment with medical informatics standards. This methodology eliminates the semantic differences between medical informatics standards. Advantages of ontological structure of NHDD are represented to be comparatively. OWL is used as ontology description language and SNOMED CT (concepts\codes), ICD 10, LOINC (codes) is used as medical informatics standards to define OBNHDD.