A rod/coil nanocomposite was prepared by a reactive mixing process of Poly(p-phenylenebenzobisthiazole) (PBZT) and Nylon66 in polyphosphoric acid (PPA). PBZT-Nylon66 block copolymers were synthesized during the reactive mixing process to act as compatibilizers of PBZT and Nylon66. The morphology and structure of the solution-cast thin film of PBZT/Nylon66 nanocomposites were investigated by using Optical Microscopy(OM), Differential Thermal Analysis(DTA), and Transmitted Electron Microscopy(TEM). PBZT were dispersed in Nylon66 matrix as fibrils which had diameters ranging from 100nm to 400nm and lengths ranging from 500nm to 2μm. The crystal behavior of Nylon66 was considerably disturbed by PBZT in the nanocomposite. Even after heating above the melting point of Nylon66, the nanocomposite exhibited no macrophase separation.