Fault diagnosis is an important research issue in rotordynamics. Unbalance is one of the most frequent faults occurs in turbomachinery. A diagnosis method is proposed in this paper to identify both locations and amounts of multiple unbalance by using the unbalance response measured at the bearing locations under one specified rotating speed. This method is suitable for on-line monitoring the gradual changes of unbalance on rotating machines, especially those required fixedly operating speeds.