The morphology of nylon 6 and polystyrene (PS) blend with styrene-maleic anhydride copolymer (SMA) as a compatibilizing agent was studied. The long-time mixing of blends exhibited slight decrease in storage modulus and larger domain size. This may be caused by imidization between amine end-group of nylon 6, and SMA produce the water, which hydrolyzes an amide group of nylon 6 and results in the decrease of viscosity. As the morphology change in blend influence on physical properties, it is found that modification of nylon 6 by SMA has a better morphology and good physical properties with shorter mixing time. However, the morphology investigation in nylon 6/PS blends reveals that the effect of mixing time was negligibly small. Addition of small amount of SMA into nylon 6/PS blend has proved to give improvement in physical properties. This behavior is based on the concentration of water derived from imidization. (c) 2006 Wiley Periodicals, Inc.