This study presents a novel capacitive-type single proof-mass 3-axis accelerometer implemented on SOI wafer. This accelerometer contains special designed gap-closing differential sensing electrodes in all sensing directions. The present SOI-based 3-axis accelerometer has four merits, (1) the proof-mass is composed of device and handle layers of SOI wafer, (2) the sensitivity is improved by the gap-closing differential electrodes design in all sensing directions, (3) the sensing gap thickness is precisely defined by the box-oxide layer of SOI wafer, and (4) the poly-refilled via is used to implement the vertical interconnection between device layer and handle layer. In application, the single proof-mass 3-axis accelerometer is fabricated and characterized. The preliminary measurement results demonstrate the sensitivities of accelerometer are 9.56mV/G (X-axis), 6.9mV/G (Y-axis) and 14.51mV/G (Z-axis). ©2010 IEEE.