The present invention relates to a seat rail structure for a motorcycle having a seat rail on a vehicle body. In this structure, the seat rail has a side member being a bent product of continuous fiber reinforced resin, the side member has: a side wall at an outer end in a width direction of a vehicle body; and an upper flange at an upper end of the side wall to protrude from the side wall inward in the width direction, the side wall has an upper fastening portion at an upper end section of a front end region, fastened to a main frame, the upper fastening portion has an upper corner edge portion straddling front edge and upper edge portions, the upper corner edge portion is arcuate, and a rear end of the upper corner edge portion is frontward relative to a front edge portion of the upper flange.