A vehicle side portion structure that includes: a pair of rockers arranged at each of two outer sides of a vehicle width direction of a floor panel of a vehicle, the rockers extending in a vehicle front-and-rear direction; and a plurality of cross-members that are arranged with length directions thereof in the vehicle width direction, both length direction end portions of each cross-member being fixed to the pair of rockers, and the cross-members being disposed to be spaced in the vehicle front-and-rear direction. A separation distance between neighboring cross-members in the vehicle front-and-rear direction is specified such that a bending reaction force of the rockers in response to an impact load applied during a side collision of the vehicle is equal to or greater than the impact load.