A good documentation or representation is important for communicating simulation conceptual models between stakeholders effectively. A good conceptual model representation may be used as a legal document in a simulation project contract; it may be used as a model description, which is crucial in a distributed simulation environment for model reusability and interoperability and, finally, it can improve the credibility of the model. This paper proposes a unified representation of simulation conceptual models. A conceptual model comprises a number of components, which can be grouped into the problem domain and the model domain. A number of diagrams and textual representations are proposed to represent each of the conceptual model components. Our intention is to initiate the discussion and development of a unified conceptual model representation that will benefit stakeholders involved in a simulation project. A case study in health-care is used to show how the proposed unified conceptual modelling can be applied in practice.