A vehicle body superstructure includes a roof side rail having a rail flange upon which a roof panel is mounted, a vertical rail wall that hangs down from the outer end of the rail flange in the vehicle width direction, a bottom rail wall that extends from the lower end of the vertical rail wall to the outside in the vehicle width direction, and a bulging section formed by allowing the bottom rail wall and the vertical rail wall to bulge toward the center in the vehicle width direction, in order to accommodate a slide rail for a sliding door. The outer end of a roof arch in the vehicle width direction is joined to the bulging section. First arch flanges are joined on the lower surface side of the rail flange. Second arch flanges are joined to the lower surface side of the of the bottom rail wall.