A various multimedia application services are developed wiht techniques of high speed networks and computer. Especially the videoconference system is important and useful in a remote discussion with multiple users. A vidoconferencing system in local area network used in corporation and university is useful and important. A standardization for it should be showed in ITU. Recommendation H.323 describes terminals, equipment, and services for videoconference over communication networks which do not provide a guaranteed Quality of Services for videoconference over communication networks which do not provide a guaranteed Quality of Service. In this paper, we introduce ITU-T H.323 which is the standardization over internet, and show a multipoint videoconferencing system and peer to peer videophone system using the ITU-T H.323.