We designed and implemented a VoIPv6 system supporting the differentiated call processing using SIP (session initiation protocol) on the IPv6 network. The VoIPv6 system is generally divided into the call control and the voice processing parts. We implemented the SIP6 which is better in simplicity, extensibility, flexibility, scalability, and mobility than H.323 in controlling the calls, as well as IPv6Phone for voice processing. Because our implementation is based on IPv6, it can use QoS (Quality of Service) and security features of IPv6. Particularly, the SIP6 proposed in this paper shows better performance because it uses the differentiated service in the call processing.