A vehicular battery mounting structure (10) includes a floor panel (14), a battery frame (30) arranged below the floor panel (14), and a bracket (40) provided on both left and right sides of a vehicle, interposed between the floor panel (14) and the battery frame (30). The bracket (40) includes a bottom wall portion (42), an inside flange portion (48) that is on an inside in a vehicle width direction, and an outside flange portion (50) that is on an outside in the vehicle width direction. A shape of the bracket is a generally hat-shape opening upward in the sectional view taken along the vehicle width direction. The battery frame (30) is indirectly or directly fixed to the bottom wall portion (42). The inside and outside flange portions (48, 50) are joined to the floor panel (14) such that a joint strength between the outside flange portion (50) and the floor panel (14) is greater than a joint strength between the inside flange portion (48) and the floor panel (14).