A vehicle side portion structure is provided that can suppress or prevent separation at a joined portion between members at a time of a vehicle side collision. At a pillar outer reinforcement, a reinforcement upper and a reinforcement lower are joined at a joined portion by spot welding or the like. A hinge reinforcement is, in a state of spanning over this joined portion, joined to the reinforcement upper and the reinforcement lower. Therefore, when tensile force is applied to the pillar outer reinforcement, shearing force that acts on the joined portion can be reduced by reaction force obtained from the hinge reinforcement. Due thereto, at a time of a vehicle side collision, separation at the joined portion can be suppressed or prevented.