In recent years, biodegradable polymers have received intensive attentions. Most of the biodegradable polymers are polyesters with poor thermal and mechanical properties, which limit their practical applications. On the other hand, the polyamide chains contain amide bonds (ƒ{CONHƒ{). The existence of hydrogen bonds between amide bonds gives polyamides good thermal and mechanical properties. However, they are not biodegradable. To combine the advantage of polyester and polyamide, poly(butylenes succinate) (PBS) and poly(hexamethylene isophthalamide-co-terephthalamide) (PA6IcoT) were reactively blended in a LIST co-rotating processor under melting conditions. The blends were fractionated into insoluble and soluble parts using chloroform as the solvent. The Fourier transform infrared spectra of these two fractions confirmed that the exchange reaction between PA6IcoT and PBS occured when p-toluenesulfonic acid was used as the catalyst. The extents of exchange reaction, average length of the various sequences, and degree of randomness of the reactive blends were calculated by the 13C-NMR analysis. It had been found that the randomness of copolymers was increased with the increase in reaction extent. Scanning electron microscopy (SEM) was employed to investigate morphology development of the reactive blends. The copolymers generated by the exchange reaction played the role of compatibilizer to improve the compatibility of blends. The size of disperse phase was significantly reduced with increasing reaction extent. Furthermore, the crystallization behavior, thermal property, mechanical property and degradation property of the resultant blends were studied and related to their chemical structure and mesoscopic structure.