A roof rack structure may include a roof rail, which is hollow, including a hook coupling portion formed at one end portion or both end portions of a lower portion of the roof rail in a width direction thereof and integrally formed to extend in a length direction of a vehicle, and a pad including a pad hook formed at one side portion or both side portions of the pad in a width direction thereof such that the hook coupling portion of the roof rail is inserted into the pad hook, the pad formed to extend in the length direction of the vehicle.