An IPv6 multihoming architecture based on the multicast concept is proposed in the paper to provide seamless media streaming services for mobile multihomed hosts, where a multihomed host is connecting to more than one mobile heterogeneous access network. The routing protocols in previous multihoming solutions have to be modified so as to meet the fault tolerant requirement, and are difficult to implement and deploy. In the proposed architecture, existing routing protocols can be adopted without any modifications. Two types of agents are designed in the proposed architecture. The multihoming agent in the mobile multihomed host assigns a multicast address to the media streaming service, and joins the multicast group through the connecting network interfaces simultaneously. The multicast agent forwards the media streaming packets received from the media server to the multihomed host through the access networks that the multihomed host is connecting with. In the paper, the proposed IPv6 multihoming architecture is implemented to verify its feasibility. Experimental results show that the proposed IPv6 multihoming architecture is capable of providing seamless media streaming service without packet loss, even during vertical handoffs.