In this paper, we present resent works on acoustic response of a MEMS resonant accelerometer. We analyzed why the resonant accelerometer reacted to external acoustic noise theoretically and showed how to reduce the acoustic response characteristics experimentally. The resonant accelerometer consists of a proof mass and a dual ended tuning fork. It behaves in the manner of a differential mode by arranging a pair of accelerometers. The mode shape of accelerometer was analyzed to find out the input mode frequency by using a finite element method(FEM) simulation. Experimental results revealed that the accelerometer reacted to the external acoustic excitation only at the input mode frequency. We showed experimentally that the accelerometer had the susceptibility of 70dB against an acoustic noise. And the results indicated that an acoustic absorber and a metal case applied to the IMU had the reducing effects of 20dB in external acoustic response.