Recently the accident of the oil effluence occurs frequently at sea. Some systems for the oil removal of the effluent oil is developed. To remove the oil by the suction device, some methods are utilized to thicken the layer of the oil. e.g. by vortex or by a flat plate at some incidence and parallel plates located perpendicularly to the current. And the float with suction inlet is used too. But the collected oil by the devices of these methods contains much water. There is another method to remove the oil. It's the method by making the oil adhere to a plate. The collected oil by this method contains little water and this is useful in the case of the thin oil layer. In the case to remove the oil by rotating discs, Authors tried to make an approximate method about the oil thickness on the plate and the suitable rotating velocity and the quantity of the removed oil. The thickness of the oil film on the plate is regard to depend on the velocity of the plate, viscosity of the oil and gravity. Two cases was studied. The one is the case of the liquid consists of only one kind of liquid. Another is that the liquid consists of two kinds of liquid. e.g. there is the oil slick on the water surface. Then we got theoretically the suitable rotating velocity and the quantity of the removed oil. They agree to the result of the experiment well.