To improve bending rigidity of a side sill against an inward load during a lateral collision while suppressing a weight increase of the side sill, a vehicle side body structure includes a side sill that has a closed cross-sectional space extending in a vehicle longitudinal direction and a center pillar. A pillar inner provided in the center pillar has a pillar inner upper and a pillar inner lower. In a longitudinal direction of the side sill, an overlapping portion in which the pillar inner upper and the pillar inner lower overlap each other in side view in the closed cross-sectional space of the side sill is provided. The closed cross-sectional space further includes sections, each of which partitions the closed cross-sectional space in the longitudinal direction. These sections are joined to the overlapping portion and an inner surface, which faces the closed cross-sectional space, in the side sill.