This paper reports a novel GaAs micromachined accelerometer based on the meso-piezoresistive effects of resonant tunneling diodes (RTDs). The sensitive unit of the accelerometer is the RTD which is located at the root of the beams. Based on the meso-piezoresistive effects of RTD, the accelerometer transduces acceleration into electrical signal output. This kind of accelerometer has been fabricated by GaAs IC surface processes and control hole etching technology. The output sensitivity and frequency characteristics of the accelerometer have been tested on the vibrating system. The result indicates that when the RTD is biased in the negative differential resistance region, the sensitivity of the suggested accelerometer is up to 90.51mV/g, and when biased in the positive resistance region, the sensitivity is 2.39 mV/g. It is obvious that the sensitivity in the negative resistance region is more one order higher than that in the positive resistance region, and the sensitivity of the accelerometer can be adjusted through changing the bias voltage. A frequency range of this structure as high as 1.5 KHz has also been achieved.