A vehicle body structure includes a floor structure 1. The floor structure 1 has a floor body 3 formed with generally-uniform sections in a vehicle's fore-and-aft direction, a dash cross member 11 connected with a front end of the floor body 3 and a rear cross member 13 connected with a rear end of the floor body 3. A side sill 5 is arranged on one side of the floor structure 1. A pillar 21 is connected with the side sill 5 through its lower end 21a. In the structure, a strength adjusting part 29 is formed in the side sill 5, for adjusting the strength of the side sill 5 in local. When the vehicle has a frank collision, the strength adjusting part 29 operates to reduce a collision reactive force generated on the side of the lower end 21a of the pillar 21 in comparison with the collision reactive force generated besides the lower end 21a of the pillar 21.