A vehicle back door structure including: a back door panel made of resin having, in at least a part of a peripheral edge thereof, a recessed portion equipped with a pair of side walls and a bottom wall that interconnects vehicle front sides of the pair of side walls, with a step portion, that has one side-wall side positioned at a vehicle rear side of another side-wall side, being formed in the bottom wall; and a reinforcement rib that is formed integrally with a vehicle rear side surface of the bottom wall, that straddles the step portion, and that bridges the pair of side walls.