IETF MANET (Mobile Ad Hoc Network) WG has standardized OLSR (Optimized Link State Routing) as its proactive routing protocol. In addition, TCP (Transmission Control Protocol) is still needed for MANET thanks to its suitability for smooth integration with the fixed Internet. In particular, TCP-Vegas is a well-known transport protocol that can efficiently take account of network condition. However, TCP-Vegas that requires an accurate BaseRTT estimation cannot be directly applied to MANET because a route change makes the estimated BaseRTT obsolete. We propose a technique to improve the performance of TCP-Vegas by considering the route change, and show the performance improvement through simulation study using the ns-2 simulator.