In this paper, we reported a MEMS-based microphone that can achieve 80 dB signal to noise ratio (SNR) or 0.1 mPa resolution over the frequency range of 2 Hz to 200 Hz. In the proposed microphone, a piezoresistive cantilever with ultra-high acoustic compliance was used as the sensing element. By realizing the ultrathin structure with large pad and narrow hinges, we were able to achieve the cantilever whose deformation to pressure is more than 200 times higher than that of the previous cantilever design. The measurement results demonstrate that the proposed microphone can measure 0.1 mPa acoustic signal with frequency down to 2 Hz. The proposed microphone is useful for measurement of low-frequency sound, which is important in various applications including photoacoustic-based gas/chemical sensing and monitoring of physiological parameters and natural disasters.