A lower vehicle-body structure of the present invention comprises a vehicle floor, a first floor cross member extending in a vehicle width direction, a second floor cross member extending in the vehicle width direction, the second floor cross member being spaced, in a vehicle longitudinal direction, apart from the first floor cross member, a side sill extending in the vehicle longitudinal direction and provided at an end portion, in the vehicle width direction, of the vehicle floor, a floor frame extending in the vehicle longitudinal direction and provided on an inward side, in the vehicle width direction, of the side sill, and attaching members for attaching a seat to a vehicle body. The attaching members are fixed to the side sill, the first floor cross member, and/or the second floor cross member.