Recently, there are a lot of studies concerned with videostreaming methods based on peer-to-peer network in order to realize efficient video services. However, a lot of these are not considering user’s real network environment, and these are not enough about efficiency in the use of network resources and device resources. On the other hand, the strategy of an appropriate quality streaming is needed in order to deal with the user’s various quality demands. In this paper, we propose PLEXCast System: Peer-to-Peer videostreaming system that deal with each user’s multiple network environments, quality demand, and dynamic change of delivery network. PLEXCast System has following functions: 1) IP unicast/multicast selecting protocol with user’s network environment, 2) contents transcoding function with user’s quality demand, 3) sub-streaming function for assuring service continuity.