In-situ polycondensation of terephthaloyl chloride and p-phenylenediamine was carried out by solution or interfacial polycondensation methods in the presence of rubbers such as styrene-butadiene triblock copolymers and acrylonitrile-butadiene randam copolymers so that a novel composite polymers of rubbers and poly (p-phenyleneterephthalamide) was obtained. Mechanical properties of rubbers were greatly improved by the incorporation of rigid rod-like polymers. In-situ polymerization of N-carboxy methyl-L-glutamate was carried out in solutions of rubbers so that a composite polymer of rubbers and poly(L-glutamate) was obtained. Mechanical properties of rubbers were also greatly improved by the in-situ polymerization, while solution blending of poly(L-glutamte) did not result in the improvement of mechanical properties.