This paper proposes a novel leakage flux cancellation technique suitable for series-parallel combined resonant circuits with asymmetric rotary transformer used for ultrasonic spindles drive. An asymmetric rotary transformer is utilized in the ultrasonic spindle in order to realize automated tool change. However, an asymmetric rotary transformer is likely to occur much leakage fluxes in secondly core due to asymmetric core structures. This large leakage inductance affects a drive circuit using a series-parallel combined resonant circuit, and the resonant characteristics in the drive circuit become very steep. In this state, the resonance circuit does not realize the desired function when the drive frequency fluctuates or the error of resonance parameters occurs. Therefore, this paper proposes a novel leakage flux cancellation technique used for ultrasonic spindle drive. The effectiveness of the proposed method is discussed from the theoretical analysis and experimental test.