To provide a vehicle body mounting structure for a fuel tank tank, which can suppress deformation of the fuel tank due to a band member while suppressing increase in weight of the fuel tank, the vehicle body mounting structure for a fuel tank includes: a band member (21) disposed along a lower surface (14) of the fuel tank (1) made of resin and having both ends secured to the vehicle body; an upper groove (31) formed in a side surface (12) of the fuel tank (1) to extend downward from an upper surface (13) of the fuel tank (1) over at least a part of the side surface (12) of the fuel tank (1); and a cushion member (26) interposed between the fuel tank (1) and the vehicle body and straddling the upper groove (31).