Abstract: To solve the communication problem of synchronous collaboration systems with heterogeneous architectures, the integration of the heterogeneous systems was discussed. A new formalized mode of synchronous collaboration system was proposed and key integration operation was defined, based on the set theory. While analyzing the integration, the agent mechanism was used to avoid the differences of resources and networks between heterogeneous collaboration systems and the multicast transport mechanism was used to link the several collaboration systems at a session. The integrative framework with four levels was developed, based on the two mechanisms. The prototype system according to the integrative framework was developed, based on web-services technology. The system realized the integration of three kinds of collaboration systems including H.323 set of standards based collaboration systems, Session initiation protocol(SIP) based collaboration systems and IP-multicast based collaboration systems. The users of the heterogeneous collaboration systems can communicate with each other.