A vehicle body rocker structure includes a plate-like inner member and a plate-like outer member that extend in a vehicle backward-forward direction and join with each other in a vehicle width direction as a structure member for constituting a rocker, wherein respective cross-sections of the inner member and the outer member include upper joint portions, lower joint portions, at least one convex portion caused to project to opposite sides joining therebetween, and concave portions disposed between the upper and lower joint portions as well as on a vehicle body upper and lower side of the convex portions, respectively, and the upper joint portions, the lower joint portions, and the convex portions of the inner member and the outer member are joined with each other, respectively and plural closed cross-sections are formed in the vehicle body up-down direction.