A scoured bridge may be suffered from earthquake loads, and be damaged more seriously relative to single seismic loads. Recent works mainly focused on the seismic fragility or reliability of scoured bridges. However, little work was performed to investigate the seismic risk and the cost of a bridge system under the double hazards in a bridge’s service life. In this work, the seismic risk and cost of a bridge under earthquake and scour were evaluated through a proposed probabilistic method. Numerical experiments are used to illustrate the usefulness of the developed probabilistic method. The findings indicate that scour significantly increases the annual failure probability and the life-cycle maintenance cost of the bridge under earthquake hazard.