Provided is a sealing structure of a fuel inlet box exhibiting good sealing characteristics without deforming a mounting surface of a vehicle body side panel. The fuel inlet box comprises a main body member and a sealing member. The main body member has a box portion, and a storage wall bulging from a side wall of the box portion and having space for storing an arm portion of a lid body. The mounting surface is interposed between a base portion of the storage wall and a flange portion, and faces the flange portion through a gap extending in a planar direction. A seal lip of the sealing member is fixed on the flange portion, extending toward the mounting surface and inclined toward an outer peripheral side of an opening. An outer basing point of a root portion of the seal lip is located in the flange portion.