A method controls tub oscillation in a drum type washing machine by utilizing a ball balancer. The method includes maintaining an rpm of a drum in a predetermined rpm level for a predetermine period of time during a dehydration operation, thereby reducing a differential rotation speed between the drum and a ball, and re-increasing the rpm, such that the tub is not subject to the oscillation that is greater than a predetermined level. The drum type washing machine adopts a single race having different ball sizes and viscosities, so that the manufacturing cost of the washing machine is reduced. The tub is prevented from being subject to oscillation greater than a predetermined level through precise calculation.