In fiber reinforced polymer composites with transcrystalline structure an interface layer can exist between the fiber and the transcrystalline area. Polymer chains orient along the fiber when the matrix consists of liquid crystalline polymers and form row structures on the fiber surface. The interface layer is not oriented and consists of crystalline aggregates, when the matrix is a flexible polymer. The interface layer can be easily etched by a chemical etchant or by ion etching, whereas the transcrystalline areas are revealed by controlling the degree of etching. As a result, the interface layer and the transcrystalline area can be well distinguished from each other by using scanning electron microscopy (SEM).