Rigid polymer networks were prepared by polycondensation of 2,5-diamino-1,4-benzenedithiol with a mixture of tereplithalic acid (TPA) and trimesic acid (TMA). The apparent density was dependent on TPA/TMA ratio and much less than that of linear PBZT (1.57 g/cm(3)), showing existence of many nano voids within the network. As the segment was so rigid, many COOH's were left around the voids. The network swelled twice in weight with E caprolactam, which was polymerized into a composite form of nylon6 impregnated rigid polymer network. Extraction of free nylon6 from the composite with formic acid showed that a quarter of nylon6 grafted directly to rigid polymer network. The grafted nylon6 could not crystallize evidenced by DSC measurements. On the other hand, particles of PBZT network (several hundred nm in diameter) were prepared by stopping the polycondensation just before gelation. A composite film was prepared with the particles swollen with epsilon-caprolactam. The ratio of PBZT network/nylon6 was 1/3 and the apparent density of the composite film was 1.23 g/cm(3) which is higher than that of a pure nylon6 film (1.16 g/cm(3)). Significant improvement in the mechanical property was observed for this composite.