A fuel-tank support structure for a motorcycle includes a left outer extending portion, a right outer extending portion, a left tank support stay, and a right tank support stay. The left outer extending portion is provided in a left main frame to extend outward in a vehicle width direction of the motorcycle. The left main frame extends rearward to diverge from a head pipe to left. The right outer extending portion is provided in a right main frame to extend outward in the vehicle width direction. The right main frame extends rearward to diverge from the head pipe to right. The left tank support stay protrudes from a fuel tank and is supported by the left outer extending portion. The right tank support stay protrudes from the fuel tank and is supported by the right outer extending portion.