A vehicle body side structure, which includes: a pillar having a closed cross section formed by jointing a pillar inner panel and an outer panel; a vehicle interior side face, on which an opening is disposed, of the pillar; a seat belt retractor to be arranged inside the pillar by being inserted through the opening; a boxy member, in which the seat belt retractor is housed to be arranged in the opening, having a flange portion and a bottom back face; and a structural foaming member for jointing at least one of the flange portion and the bottom back face to an inner surface of the pillar.
