We have proposed a new nondestructive inspection method for fiberglass-reinforced plastic mortar (FRPM) pipes using microwave guide-mode propagation and photonic techniques. This method is based on the precise measurement of a microwave guided-mode propagated along a FRPM pipe-wall by use of an electro-optic (EO) sensor. In the previous research, we have confirmed that microwave can propagate along the FRPM pipe-wall as a guided-mode, and the propagated microwave transmission characteristics through the FRPM pipe are affected by defects or cracks in FRPM pipes. By measuring electric field distributions by use of an EO sensor precisely, we believe that we can detect smaller defects or cracks in/on the FRPM pipe nondestructively.