A washing machine and a control method thereof are provided, which control a rotational speed of a rotary tub (or revolutions per minute: RPM of a motor) according to a vibration level thereof to attenuate a vibration of the rotary tub. The washing machine includes the rotary tub, the motor, a vibration detecting unit and a control unit. The motor is linked to the rotary tub to be supplied with drive power and rotates the rotary tub. The vibration detecting unit detects the vibration level of the rotary tub using a variation of the drive power supplied to the motor when the motorrotates. The control unit controls a current rotational speed of the motor to be increased, maintained or decreased according to the vibration level of the rotary tub detected by the vibration detecting unit.