In cowling structure for an outboard motor, a through hole is formed below an upper-cowling joining surface of a lower cowling; control cables are supported with a cable supporting groove of a back side plate, and the back side plate is fixed to the through hole; a sealing member that is covered on the outside of the control cables, is fitted into the through hole; a groove of a front side plate is placed around the control cables, and the front side plate is set onto the sealing member; and the sealing member is fixed to the lower cowling by a bolt together with the front side plate. The cowling structure for an outboard motor can prevent water intrusion by removing a notch on an upper-cowling joining surface of a lower cowling.