Interface failure plays an important role in determining the mechanical properties of polymer based fiber reinforced composite materials [1]. Results obtained from a study concerning the effect of matrix-fiber interfacial bonding on the transverse bending properties of glass fiber reinforced polybutylene terephthalate (G/PBT) unidirectional (UD) composites are presented in this paper. Six types of specimens were manufactured using three different processing methods, namely reaction-based resin, prepreg and commingled yarn systems. The transverse bending properties of the UD composites were measured. Furthermore, the tension failure zones after the transverse bending tests were examined using scanning electron microscopy (SEM) fractography analysis. Additionally, the quality of the composites was evaluated using complementary microscopic techniques (optical microscopy, OM and SEM).