Structure of a vehicle body rear part in which a back door opening section around which a closed cross-sectional structure is provided wherein the vehicle body rear part includes rear lamp house panels, a back panel section and a back door opening section arranged to incline obliquely such that a lower part is located further toward a vehicle back than an upper part. In the structure, a tail end member extending along a vehicle width direction is coupled to lower side corner portions of the closed cross-sectional structure located on both the left and right sides of the back door opening section, swelling sections extending further outward than the lower side corner portions of the closed cross-sectional structure are provided on both the left and right sides of the tail end member, and the swelling sections are joined to the rear lamp house panels and the back panel section.