Fast scanning is highly desired for both ultrasound and photoacoustic microscopic imaging. Limited by water environment required for acoustic propagation, traditional mircoelectromechanical system (MEMS) scanning mirrors could not be widely used. In this paper, a new water-immersible scanning mirror microsystem has been designed, fabricated and tested. Polymer hinges were employed to achieve reliable under water performance. Two pairs of high strength neodymium magnet disc and three compact RF choke inductor were used to actuate mirror module. Experimental results show that the fast axis can reach a mechanical scanning angle of ±15° at the resonance frequency of 350 Hz in air, and ±12.5° at the resonance frequency of 240 Hz in water, respectively. The slow axis can reach a mechanical scanning angle of ±15° at the resonance frequency of 20 Hz in air, and ±12.5° at the resonance frequency of 13 Hz in water, respectively. The two scanning axes have very different resonance frequencies, which are suitable for raster scanning.