The Clinical Element Model (CEM) is an information model designed for representing clinical information in EHR systems across organizations. The current representation of CEMs does not support formal semantic definitions and therefore it is not possible to perform reasoning and consistency checking on derived models. This paper introduces our efforts to represent the CEM specification using the Web Ontology Language (OWL). The CEM-OWL representation connects the CEM content with the Semantic Web environment, which provides authoring, reasoning, and querying tools. This work may also facilitate the harmonization of the CEMs with domain knowledge represented in terminology models as well as other clinical information models such as the openEHR Archetype Model. We have created the CEM-OWL meta ontology based on the CEM specification. A convertor has been implemented in Java to automatically translate all the detailed CEMs from XML to OWL. A panel evaluation has been conducted, and the evaluation results show that the OWL modeling can faithfully represent the CEM specification and represent patient data.