A floor structure for a vehicle includes: a center floor panel; a plurality of seat crossmembers extending in a width direction of a vehicle; a rail member disposed to be orthogonal to the plurality of seat crossmembers; a pair of side sills disposed on both sides of the center floor panel; and a pair of battery mounting beams coupled to the pair of side sills, respectively, wherein each battery mounting beam is coupled to an inboard sidewall of each side sill, and cylindrical nuts for mounting a battery assembly are individually disposed on the battery mounting beams and the seat crossmembers.