Provided is a vehicle body bottom structure capable of restricting retraction of a front pillar by improving absorption performance for a collision load at a time of a narrow offset collision. The vehicle body bottom structure includes a dash lower for partitioning a vehicle compartment and a power mounted room as well as partitioning the vehicle compartment and a wheel house, a front pillar erected at a vehicle-widthwise end portion of the dash lower, and a gusset bridged between the dash lower and the front pillar, wherein the gusset is joined to the dash lower at one end thereof, and is spaced further from the dash lower the nearer to the front pillar, to be joined to the front pillar at the other end thereof, and wherein a crushing space is formed in a portion surrounded by the dash lower, the front pillar, and the gusset.