Method and apparatus for determining data encoding format in RMI-IIOP messages. Embodiments may provide a mechanism to use Java serialization rather than, or as an alternative to, CORBA Common Data Representation (CDR), for the marshaling and unmarshaling of data in RMI-IIOP message exchanges. In one embodiment, a server-side Object Request Broker (ORB) may be configured to support the encoding of data in RMI-IIOP messages in accordance with CDR encoding and Java serialization encoding. In one embodiment, an Interoperable Object References (IOR) published by the server may include information that indicates which encoding type(s) are supported by the server-side ORB on the server that hosts the associated object. A client-side ORB may optionally use Java serialization or CDR as the data encoding format for RMI-IIOP messages to invoke the associated object on the server. Each RMI-IIOP message may include an indication of which encoding type is used in the message.