Satellite communication is able to provide wide bandwidth, and satellite-based Internet access is expected to be a high speed Internet access method of the next generation. However, the propagation delay of a satellite that TCP performs window based flow control and most communicating hosts use the default window size such as 8 Kbytes through 24 Kbytes. To deal with this problem, we propose a TCP gateway for satellite-based Internet access. The communication throughput of TCP is improved without any modifications to equipment and terminals of subscribers by introducing this system only at a satellite earth station. In this paper, we describe the protocol architecture of the TCP gateway and its performance by comparing with conventional methods. The results of a performance evaluation show that the proposed TCP gateway can provide more than 20 times higher throughput than communication without it over a link with 6 Mbps bandwidth and 350 msec round trip time.