As the size of wind turbines increases, the early detection of structural instability becomes increasingly important for safety. This paper introduces a fiber Bragg grating-based sensing system for use in multi-MW scale wind turbine health monitoring, and describes the results of preliminary field tests of dynamic strain monitoring of the tower structure of an onshore wind turbine. For this research, the Korea Institute of Energy Research (KIER) and the FiberPro, Inc. cooperated on the development of a wavelength division multiplexing (WDM) Bragg grating sensing system for high-speed strain sensing. The FBG interrogator thus developed can be used in the sensing of high-speed vibration as well as low-speed dynamic strain. In the case of high-speed sensing, the interrogator allows a sampling ratio of over 40 kHz for six linearly arrayed FBG sensors per channel. To monitor the dynamic strain behavior of the tower and substructure of onshore and offshore wind turbines, 41 FBGs were installed on the supporting structures of the wind turbines. As a result, the Bragg grating sensing system showed stable, accurate performance in the thermal chamber test and good dynamic strain sensing performances during the strain monitoring of the tower structure at the Woljeong test-bed wind turbine in Jeju Island.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.