A watertight structure for a spliced portion includes a container that has an open top adapted to receive a spliced portion of electrical wires and that is elongated in a longitudinal direction of the electrical wires, and a lid to be mounted on the container. The container is provided with a bottom wall and upward inclined portions that extend in a longitudinal direction. The container is provided with a spliced portion positioning section having a narrow width. The spliced portion positioning section is provided on opposite outer sides with receiving portions to be engaged with locking pieces projecting from the lid.