An internal combustion engine exhaust system supporting structure includes a body fastening portion, an exhaust fastening portion, a bracket, and a stay. The body fastening portion is provided on a power plant or a vehicle body located on a side of an exhaust passage extending from an internal combustion engine to a rear of a vehicle so that exhaust emissions flow from the internal combustion engine to the rear of the vehicle. The bracket is fastened to the body fastening portion. The stay is fastened to the exhaust fastening portion and has lower stiffness than the bracket. The bracket and the stay are fastened to each other at a connecting portion so that a vertical distance between the exhaust fastening portion and the connecting portion in a vertical direction is greater than a vertical distance between the body fastening portion and the connecting portion in the vertical direction.