Abstract: A structure arranged under a floor panel for mounting a tank to be charged with a pressurized-fuel such as natural gas and liquefied petroleum gas in a motorcar of front engine --front drive type is provided. The pressurized-fuel tank installation structure in a motorcar includes a chassis frame formed in a frame-shape for surrounding and supporting the pressurized-fuel tank and attached to a lower surface of the car-body from underside of the floor panel, the pressurized-fuel tank being positioned in the frame-shape and fitted to the chassis frame integrally; a rear wheel suspension provided on the chassis frame; and a pipe arranged along a lower surface of the floor panel for connecting the pressurized-fuel tank and an internal combustion engine with each other.