To provide a fuel tank arrangement structure of a vehicle that can compatibly secure tank capacity, vertical comfortableness in the cabin, and foot space of an occupant, especially becomes an advantageous structure also to a side collision, and does not damage seat arrangement.

In the fuel tank arrangement structure of the vehicle, a plurality of occupant seats 9 and 10 are arranged longitudinally. A tunnel section 8 that is projected upward and toward the inside of the cabin and has a shape in the vehicle width direction of which the rear part is narrower than the front part is disposed in the center section in the vehicle width direction of a floor panel 4 forming the lower surface of the cabin 2. The space in the tunnel section 8 under the floor panel 4 is provided with the fuel tank 40 having a shape in the vehicle width direction of which rear part is narrower than the front part correspondingly to the shape of the tunnel section 8. A front seat 9 is disposed above a wide section 8a wide in the vehicle width direction of the tunnel section 8, and the rear seat 10 is disposed above narrow sections 8c and 8d narrow in the vehicle width direction of the tunnel section 8.