Abstract. UnifyingTheoriesofProgramming(UTP)canprovideaformalsemantic foundation not only for programming languages but also for more expressive specification languages. We believe UTP is particularly well suited for presenting the formal semantics for integrated specification languages which often have rich language constructs for state encapsulation, event communication and real-time modeling. This paper uses UTP to formalise the semantics of Timed Communicating Object Z (TCOZ) and captures some TCOZ new features for the first time. In particular, a novel unified semantic model of the channel based synchronisation and sensor/actuator based asynchronisation in TCOZ is presented. This semantic model will be used as a reference document for developing tools support for TCOZ and as a semantic foundation for proving soundness of those tools.