A vehicle body bottom structure includes a dash lower for separating a vehicle compartment from a power mounted room as well as separating the vehicle compartment from a wheel house, a front pillar which is erected at a vehicle-widthwise end portion of the dash lower, and a gusset which is bridged between the dash lower and the front pillar. The gusset is joined to the dash lower at one end thereof, and is spaced apart from the dash lower as the gusset approaches the front pillar, to be joined to the front pillar at the other end thereof, and a crushing space of a substantially triangular shape in a plan view is formed in a portion surrounded by the dash lower, the front pillar, and the gusset.