Knowledge modelling techniques are widely adopted for designing knowledge-based systems (KBS) and these systems are important for knowledge management. This paper argues the need and importance of adopting Unified Modeling Language (UML) for knowledge modelling through the profile extension mechanism. KBS are developed using knowledge engineering (KE) techniques that are often similar to software engineering (SE), and both domains emphasise the use of conceptual models in designing software systems. Most of these knowledge models heavily rely on modelling notations used in software engineering; in this the UML is widely adopted. UML can be formally tailored for knowledge modelling by creating a UML profile for knowledge modelling