In a vehicle body side structure, a tailor welded blank is used for forming an outer panel assembly consisting of a frame structure, and a center pillar assembly is connected vertically between a roof side rail and a side sill outer of the outer panel assembly. The center pillar assembly is made of a material having a higher mechanical strength than most of the outer panel assembly. Thereby, the stamp forming process can be simplified, and a required mechanical strength can be ensured in a favorable manner. In particular, the center pillar assembly may include a center pillar outer made of material having a higher mechanical strength than at least a part of the outer panel assembly, the center pillar outer being attached to an outboard side of the side sill outer at a lower end thereof and to an inboard side of the roof side rail at an upper end thereof.