By adding a small amount of acid treated multi-walled carbon nanotubes (MWCNTs) into poly(p-phenylene sulfide)/polyamide 66 (60/40 w/w) blends, the morphology was found to change from sea-island to co-continuous structure. As the MWCNT content was increased, the morphology came back to sea-island but with increased domain size. It was very interesting to note that the MWCNTs were found to be selectively located in the PA66 phase, and their assembling determines the final morphology of PPS/PA66 blends. A dendritic contacted MWCNTs network was formed at low load, which leads to the formation of a co-continuous structure, and isolated MWCNT aggregates were observed at high load, which leads to the formation of sea-island morphology. Since the properties of multiphase polymeric materials are not only determined by the properties of the component polymers, but also by the morphology formed, our work indicates that the behavior of phase-separating polymer blends containing MWCNTs can be exploited to create a rich diversity of new structures and useful nanocomposites. (c) 2006 Elsevier Ltd. All rights reserved.