The present invention relates to a duct for a ship. A duct main body is installed between a propeller and a stern of a ship. An upper end or lower end of the duct main body is positioned at 20 percent or more or less of propeller diameter with respect to an axis of the propeller. The shape of the duct at a portion attached to the stern has an angle of attack to reduce the speed of flow. Therefore, the duct for a ship can generate pressure recovery on the stern side and increase propeller efficiency by varying the shapes of the upper end and the lower end of the duct main body.
