Asynchronous Transfer Mode (ATM) has been selected as the core technology in high speed networks. This paper presents an object-oriented model OOATM for the development of ATM protocols. The model consists of four kinds of entities: (1) interface entities provide service primitives to upper layer and generate the corresponding protocol data unit (PDU), (2) connection entities manipulate communication services, (3) state entities deal with state transitions and the corresponding services, and (4) message entities describe the format and contents of the Protocol Data Unit(PDU) in a protocol. We have constructed a class library for these entities and the paper presents an approach to construct an ATM protocol with the library. An example of constructing a Signalling protocol shows that this approach provides a high level modeling, and reusability. Keywords: ATM, object orientation, Signalling, protocol, class hierarchy