This paper presents some results of studies on application of a monitoring system using Micro Electro Mechanical System (MEMS) sensors in order to measure deformations of a retaining wall. The MEMS sensors have three advantages which are compact, lightweight, and inexpensive. In this paper, the authors propose that using the supports system, the precision of the sensor network system gets higher than before. Using wireless communication between the transmitter and receiver in this system, the data observed by the MEMS sensor is transmitted to the base station directly, and the distance is approximately 500m with good visibility and about 300m with vegetation. The authors applied this system to monitoring an actual retaining wall under construction. It is concluded from the result that the MEMS sensor could measure very small deformations of the retaining wall and the small change of an inclination had been affected by a series of external factors such as rainfalls and an earth pressure from the back of the wall.