This article describes the development of a fiber optic accelerometer based on Fiber Bragg Gratings (FBG). The accelerometer, designed for the structural health monitoring of bridges, utilizes a lumped mass attached to a stretched FBG. Acceleration is measured by the FBG in response to the vibration of the fiber optic mass system. The wavelength shift of FBG is proportional to the change in acceleration, and the gauge factor pertains to the shift in wavelength as a function of acceleration. The accelerometer was first evaluated in laboratory settings and then employed in a demonstration project for condition assessment of a bridge. Laboratory experiments included a series of low frequency low amplitude sinusoidal excitation tests to evaluate the sensitivity and frequency resolution of the proposed sensor. Two series of multiplexed FBG accelerometers were utilized to assess the dynamic properties of a bridge under ambient vibration conditions. The Frequency Domain Decomposition method was employed to identify the mode shapes and natural frequencies of the bridge. Results were compared with the data acquired from the conventional accelerometers.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.