In this paper, we propose an ultrasensitive optical Micro-Electro-Mechanical-System (MEMS) accelerometer based on wavelength modulation, using one dimensional photonic crystal (PC). An air-dielectric multi-layer Photonic Band Gap (PBG) material, a typical Laser diode (LD) light source, a Photo Diode and integrated optical waveguides build up the optical sensing system of the proposed device. Functional characteristics of the proposed accelerometer are as follows: a mechanical sensitivity of , an optical sensitivity of  and a linear measurement range of  to . Regarding to the mentioned characteristics, the proposed MOEMS accelerometer is suitable for a wide range of applications such as inertial navigation, consumer electronics, automotive, etc.