Provided is a lower vehicle body structure that improves the support rigidity of a vehicle body floor for supporting seat rails. The lower vehicle body structure of the present invention includes: a vehicle body floor (2); a first floor beam (14) extending along the vehicle width direction and having a closed cross-section structure; a second floor beam (16) parallel to the vehicle front and rear direction. The first floor beams (14) are arranged at intervals and have a closed cross-sectional structure along the vehicle width direction; the side beams (4) are arranged at the ends of the vehicle body floor (2) in the vehicle width direction and along the vehicle front-rear direction extending and having a closed cross-sectional structure; the floor frame (12), which is arranged on the inner side in the vehicle width direction compared with the side beam (4), extends along the vehicle front-rear direction and has a closed cross-sectional structure; and the mounting parts (65, 66, 68, 69), for installing the seat to the vehicle body. Mounting members (65, 66, 68, 69) are fixed to the edge beams (4), the first floor beam (14), and / or said second floor beam (16).