Abstract. UML-RT is an extension of UML for modelling embedded reactive and real-time software systems. Its particular focus lies on system descriptions on the architectural level, de ning the overall system structure. In this paper we propose to use UML-RT structure diagrams together with the formal method CSP-OZ combining CSP and Object-Z. While CSP-OZ is used for specifying the system components themselves (by CSP-OZ classes), UML-RT diagrams provide the architecture description. Thus the usual architecture speci cation in terms of the CSP operators parallel composition, renaming and hiding is replaced by a graphical description. To preserve the formal semantics of CSP-OZ speci cations, we develop a translation from UML-RT structure diagrams to CSP. Besides achieving a more easily accessible, graphical architecture modelling for CSP-OZ, we thus also give a semantics to UML-RT structure diagrams.