A vehicle-mounting structure for a fuel cell system of the present invention has a fuel cell, and a hydrogen-related component in which hydrogen to be supplied to the fuel cell flows. In the structure, the fuel cell and the hydrogen-related component are mounted in a space on a front portion in a vehicle body, a hood covering a top opening of the space is inclined downward from a rear side to a front side in the vehicle body, and the hydrogen-related component is placed at a position on the rear side and upper side of the fuel cell in the vehicle body.