In a vent control valve for a fuel tank, a housing receiving a float assembly therein is provided with a communication hole passed across a wall of the housing, and an opening of the communication hole facing an interior of the housing is directly exposed to an interior of the housing when the float assembly is in a low position and overlaps with a peripheral wall of the float assembly when the float assembly is in a high position. By suitably selecting the size of the communication hole and/or the number thereof, a desired delay in the dropping of the liquid fuel level in the housing following the filling up of the fuel tank can be achieved. Thereby, overfilling of the fuel tank can be avoided. As the float assembly drops to such an extent as to clear the communication hole, the fuel vapor is allowed to flow more freely into the interior of the housing via the communication hole, and this causes an increase in the speed of the float to drop. Thereby, the venting of the fuel tank can be resumed at an appropriately earlier stage following the filled up state of the fuel tank. Thus, the closing and opening of the communication with the exterior of the fuel tank can be accomplished even when the vertical dimension of the housing is relatively small.