Nondestructive testing method for fiber orientation and fiber content in fiber reinforced composites, such as CFRP and GFRP, is examined by using 4 GHz microwave. Fiber direction, misorientation, and fiber content are detectable for unidirectional CFRP. In this apparatus, transmitted wave is divided into two cross components and their difference and/or ratio is measured, so that the sensitivity of detecting the fiber orientation is improved and change of the fiber direction is detected separately from that of the fiber content. The sensitivity of the detection is especially good for the fiber direction and misorientation in such thin CFRP samples as less than about 1 mm in thickness. This method, therefore, is found to be preferably useful to check fiber orientation of intermediary materials such as prepreg rather than end constructions or products. The sensitivity of detection for GFRP is rather low in comparison with CFRP, because the difference of electrical property between matrix resin and glass fiber is small. Theoretical formulations and calculations for transmission and reflection of electromagnetic wave in anisotropic layered material are performed, and good agreement with the experimental results is obtained.