This paper presented a novel resonant frequency tracking control method for electronic ballast of electrodeless lamp. The proposed method enables the operation frequency of the electronic ballast to continuously track the resonant frequency of the resonant tank by detecting the phase difference between input voltage of resonant tank and resonant capacitor voltage . Using the proposed control method, the ballast can be optimized to operate with its maximum power capability and guarantee good load matching, even when the resonant tank parameters vary. The detailed implementation of the controller was presented in this paper. Simulation and experimental results verify the performance of the proposed control method.