: Computer Assisted Surgery seeks data from various sources related to surgical knowledge, which is mostly represented in the form of discrete databases. However, databases serve as data storage mechanism rather than knowledge representation system. As CAS is becoming more common for various types of surgical interventions, there is a need for representation, storage and processing of surgical knowledge in a more structured manner. The traditional way of using databases to store the data needs to be augmented with a conceptual representation mechanism, which can serve as a bonding layer among the various sources of surgical knowledge. Ontological modelling provides the means to represent conceptual knowledge using expressive formal logics. The scope of this paper is to present how CAS knowledge can be represented using ontological modelling, and make use if it in the real time applications in the Operating Room.