Monitoring the health of glass or carbon fiber reinforced polymer under dynamic loading conditions is still a challenge. When metals are tested under dynamic loading conditions, usually a single crack is a source of the failure in the material. On the other hand, composite materials include several damage modes such as transverse cracking, delamination and splitting under the dynamic loading and all of them contribute ultimate failure of the material. Due to the complexity of the damage in composite materials, it is very hard to estimate health or damage state of composite materials. In this study, we propose the usage of a novel embedded biaxial Fiber Bragg Grating sensor system to track the evolution of Poisson's ratio which can be employed as a reliable damage index in composites. The fatigue experiments on specimen made of biaxial glass fiber infused with resin transfer molding system have shown that signal from novel embedded biaxial sensor system can be easily collected to evaluate Poisson's ratio. The current study also indicates that the evolution behavior of Poisson's ratio is consistent with other fatigue parameters such as temperature, force and strain energy that show very rapid change in the first region of fatigue with respect to number of cycles.