This study presents a novel fiber optic sensing system for monitoring debris flows. Thanks to their light weight, immunity to electromagnetic interference, high sensitivity, and very low optical loss, fiber optic sensors can be potentially utilized to monitor debris flows, which usually occur in mountainous regions far from available electricity. The ground vibrations caused by debris flows can be sensed by a Fiber Bragg Grating (FBG) Accelerometer (Gavea Sensor GS 6500) and the associated light source, and data logger are provided by a Braggscope (Fiber Sensing FS 5500). Four FBG Accelerometers were deployed along the Ai-Yu-Zi Creek and the Chu-Shui Creek in Nan-Tou County, Taiwan, respectively; and the Braggscope was located at the front data-receiving center. The calibration experiment was carried out to compare the performance of FBG accelerometer with other sensors used for detecting debris flows, such as geophone and microphone. The signal-to-noise ratio (SNR) of FBG accelerometer was higher than that of geophone, while the two instruments sensed the same vibration source. The results showed that fiber optic sensing technique could be used as an alternative for monitoring debris flows.