Filament wound pressure tanks are under high internal pressure during the operation and it has the complexity in damage mechanism and failure modes. For this reason, it is necessary to monitor the tank through its operation as well as during the whole fabrication process. A large number of sensors must be embedded into multiple positions of the tank from its fabrication step for monitoring the whole tank. Fiber optic sensors, especially fiber Bragg grating (FBG) sensors are widely used for various applications because of good multiplexing capabilities. However, we need to develop the embedding technique of FBG sensors into harsh inner environment of the tank for the successful embedment. In this paper, we studied the embedding technique of a number of FBG sensors into filament wound pressure tanks considering multiplexing and conducted in situ structural health monitoring of filament wound pressure tanks during water-pressurizing test using embedded FBG sensor arrays. From the experimental results, it was demonstrated that FBG sensors can be successfully adapted to filament wound pressure tanks for their structural health monitoring by embedding.