Provided is a vehicle body rear part structure. The vehicle body rear part includes a rear pillar, a damper housing and a gusset. The rear pillar forms a closed cross section by joining a pillar outer to a pillar inner. The gusset connects the damper housing and the rear pillar. The pillar inner is separated into a front inner plate and a rear inner plate with a position above a top wall of the damper housing as a boundary. Bulkhead parts are formed on end edges of the front inner plate and the rear inner plate that face a separation part by bending to have a substantially L-shaped cross section to reinforce the closed cross section between the pillar outer and the bulkhead parts. An upper part of the gusset is combined to the rear pillar to close the separation part.