Abstract: In a vehicle body side portion structure, a center pillar includes an upper pillar section joined to a roof side rail and a lower pillar section joined to a side sill, the upper pillar section including a metallic pipe having a high-strength steel plate, has a substantially constant cross-sectional shape, and is convexly curved outwardly in a vehicle width direction, the lower pillar section is formed by two pressed components including a steel plate having lower strength than the steel plate of the hollow metallic pipe of the upper pillar section and are joined to each other into a closed cross-sectional shape, and the upper pillar section is joined to the two pressed components such that the lower edge part of the upper pillar section is inserted within a section configured by the two pressed components of the lower pillar section and having the closed cross-sectional shape.