The composites of rigid rod poly(phenylene terphthalamide) (PPTA) and flexible nylon 6 were prepared by using an in situ polymerization.The anion of PPTA was used as the initiator for the anionic polymerization of caprolactam of form the nylon 6 matrix.SEM photographs showed that PPTA was dispersed in the matrix in a form of microfibril with a diameter of 50～100nm.The microfibril serves as the reinforcing agent in nylon matrix and leads to a nearly two fold increase in modulus

64% increase in tensile strength and a significant reduction in strain to break.The DMTA results also shoued that the mechanical properties of PPTA/nylon 6 composites were greatly inmproved.