A support structure of a vehicle body may include left and right inner side sills forming frames of lower portions of sides of the vehicle body in a width direction of the vehicle, an intermediate floor connecting a center floor forming a center portion of floors and a rear floor of the vehicle body, left and right rear side members forming frames of rear portions of the vehicle body in the length direction, and one end portions of inner sides of the left and right rear side members, respectively connected to both end portions of the intermediate floor in the width direction, and left and right front upper support members extending in the width direction, mounted on an upper surface of the intermediate floor, and one ends of the left and right front upper support members, respectively connected to the left and right inner side sills.