Nylon-6 was reinforced by two semi-rigid aromatic polyamides, poly(p-diphenylmethyl terephthalamide) (PMA), and poly(p-diphenyloxide terephthalamide) (POA), and also one wholly-rigid aromatic polyamide, poly(m-phenylene isophthalamide) (PmIA) by physical blending and chemical copolymerization using p-amino phenyl acetic acid (P-APA) as a coupling agent. From the results of differential scanning-calorimetry, it was shown that both the polyblends with semi-rigid and wholly-rigid polyamides exhibited a glass transition temperature, T(g), higher than that of nylon-6 homopolymer. It also showed that the T(g)s of wholly-rigid polyblends were higher than those of semi-rigid polyblends. Nevertheless, the multiblock copolyamides appeared to have even higher T(g) and T(m), and better thermal stability. Morphological observations revealed that all the polymer alloys (polyblends and copolymers) were a dispersed phase structure, although the multiblock copolyamides were more homogeneous and compatible. Based on wide-angle X-ray diffraction, it was found that the polyblends had two diffraction peaks, i.e. 2theta=20.5-degrees and 24-degrees. However, the multiblock copolyamides had only one peak at 2theta=20-degrees, evidently indicating a new crystal structure of the multiblock copolyamides formed. For the mechanical properties, it was found that the multiblock copolyamides had a more significant reinforcing effect than those of polyblends, especially those copolymerizing with wholly aromatic polyamides.