Abstract: BitTorrent-based applications incur massive cross-ISP traffic which heavily decreases Internet efficiency. Taking into account BitTorrent protocol specifications and connection structure among different ISPs, this paper proposes an ISP-aware BitTorrent traffic optimization scheme which is called STracker. STracker is composed of tracker proxies in different ISPs. Tracker proxies are connected with a P2P protocol. Tracker proxies perform node management and biased neighbor allocation. Therefore, the cross-ISP traffic is reduced. Analysis and simulations show that STracker can efficiently reduce the cross-ISP traffic while the download time is not increased. STracker can reduce the operation cost of ISPs and improve the efficiency of Internet efficiently.