An outboard motor has an under cover forming a lower part of an engine room in which an engine is installed. The under cover has a pair of right and left cover members detachably connected together along opposing vertical edges thereof; an opening formed in at least one of the cover members for allowing access to the engine. The opening is vertically spaced from an upper edge of the under cover and extends contiguously from the vertical edge of the at least one cover member. A lid made of elastic material is attached to an outer surface of the under cover so as to close the opening of the under cover, the lid being elastically deformable to open and close the opening.