A high-Q microwave photonic filter using a semiconductor optical amplifier (SOA)-based mode-locking fiber ring laser is proposed, analyzed and experimentally demonstrated. The proposed microwave photonic filter can realize a high-Q frequency response, it is compact without an optical source, and it can be easily tuned by adjusting an optical variable delay line in a ring cavity. A result with a Q-factor of about 236 and a rejection ratio of about 45 dB is obtained. The measured results and the theoretical estimations agree very well.