Information systems of automobiles in the future will have several broadband wireless access systems to the Internet. Among them, DSRC (Dedicated Short Range Communications) is attractive as broadband mobile access system, though coverage will be limited. To extend coverage in effect from viewpoint of users, system can be effective in which terminals share data received from the Internet with other terminals located out of coverage using inter-vehicle communication. In this case, routing protocol of multi-hop inter-vehicle communication network should achieve high throughput with low control overhead when there are many terminals and large amount of data traffic are offered to the network. However, conventional routing protocols using only peer-to-peer communication are difficult to meet these requirements. This paper presents a cellular-assisted proactive routing protocol for multi-hop inter-vehicle communication network. In the method, each terminal is equipped with both ad hoc mode wireless LAN and cellular system capability. It sends its link state packets to a control node provided in a fixed network using cellular system, and the control node sends link state packets to all terminals using multicast function of cellular system to reduce number of packets transmitted. Simulation using straight road model confirmed that number of transmitted control packets in the proposed method reduces compared with conventional on-demand routing protocol, and amount of reduction increases according to increase of demands for data connections arise in the network.