Data transfer of large files over the Internet is often performed using Peer-to-Peer (P2P) technology. BitTorrent is the most popular P2P content distribution application. In general, BitTorrent users have much higher download bandwidth than upload bandwidth. It leads to bottleneck problem under the lack of the upload bandwidth, and it drastically degrades the performance of the overall system. In this paper, we propose a method to utilize idle upload bandwidth of helper in order to improve the file sharing efficiency on the BitTorrent. We also evaluate the efficiency of the proposed method by using simulation.