In a cable insertion structure for an outboard motor, a pawl section and a supporting section of a resinous cap are inserted from the inside of a cowling into a communicating hole of a rubber grommet, and the pawl section is fitted into a recess. Then, the communicating section of the rubber grommet is sandwiched between the pawl section and the pressing section, and thus the resinous cap is fixed to the rubber grommet. In the above-described state, a cable is inserted from an insertion hole of the resinous cap into a cable housing section of the rubber grommet. A clip band is fastened to a groove of the cable housing section to fix the cable housing section to the cable. The cable insertion structure for an outboard motor prevents a rubber grommet from coming off even when an external force that pulls the cable is applied.