In a vehicle body side structure, an outer reinforcement lower is configured as a divided structure of a reinforcement body and a divided patch that are joined to each other at a joint portion located in a corner portion. Accordingly, when a load from a front wheel is input to a front pillar at the time of a small overlap collision, the outer reinforcement lower can be bent at the joint portion near the root of the outer reinforcement lower. Consequently, the bending moment that is transmitted to a rocker outer reinforcement can be reduced and therefore longitudinal bending deformation of the rocker outer reinforcement can be suppressed. As a result, deformation of a vehicle compartment can be suppressed.