A procedure for estimating risk of road structures subjected to seismic ground motion and subsequent tsunami is proposed. In the 2011 Great East Japan earthquake, many bridges and embankments were severely damaged due to the strong ground motion and/or subsequent tsunami. The damage to these structures caused significant economic losses associated with the reconstruction and disruption of the road network. Given a limited budget, it is important to estimate the economic loss due to the damage to structures in road networks and determine the retrofitting prioritization for effective risk mitigation. In an illustrative example, the risk of road networks under both seismic and tsunami hazards caused by the anticipated Nankai Trough earthquake is estimated. The numerical results show that the retrofitting prioritization can be determined by comparing the risk of road networks.