This paper proposes an ontology-based approach of modeling clinical pathway workflows at the semantic level for facilitating computerized clinical pathway implementation and efficient delivery of high-quality healthcare services.A clinical pathway ontology(CPO)is formally defined in OWL web ontology language (OWL)to provide common semantic foundation for meaningful representation and exchange of pathway-related knowledge.ACPO-based semantic modeling method is then presented to describe clinical pathways as interconnected hierarchical models including the top-level outcome flow and intervention workflow level along a care timeline.Furthermore,relevant temporal knowledge can be fully represented by combing temporal entities in CPO and temporal rules based on semantic web rule language(SWRL).An illustrative example about a clinical pathway for cesarean section shows the applicability of the proposed methodology in enabling structured semantic descriptions of any real clinical pathway.