A nozzle for a cleaner includes a nozzle body having a suction passage in which air flows. A water tank is detachably mounted on the nozzle body, and a rotation cleaning part is rotatably supported at a lower side of the nozzle body to receive water from the water tank for cleaning a floor. The water tank includes an outlet through which water is discharged, a valve configured to open and close the outlet, and an air hole configured to introduce outside air into the water tank. An air hole operation part is movably installed on the water tank to open and close the air hole.