Lower vehicle-body structure of vehicle

A lower vehicle-body structure of a vehicle can improve the support stiffness of a suspension supporting portion to reduce floor vibration. Arm front-end supporting portions (20, 20A), each supportinga front end portion (12) of a trailing arm (11) of a rear suspension (10), are formed on lower portions of rear frames (6) extending in a vehicle longitudinal direction, and each arm front-end supporting portion (20) includes a squared U-shape portion (21, 21A) including an outer wall portion (30r), inner wall portions (23, 23A) and front wall portions (24, 24A), with a rear side being open whenviewed from the bottom, and an extending outer wall portion (30f) extending from the outer wall portion (30r) to in front of the front wall portions (24, 24A). The outer wall portion (30r) and the extending outer wall portion (30f) are formed by a side sill inner portion (3a) joined to each rear side frame (6). Also, each arm front-end supporting portion includes an extending inner wall portion (40, 26) extending from the