Abstract The migration of multi-walled carbon nanotubes (MWCNTs) from the thermodynamically favored polycarbonate (PC) phase to the acrylonitrile-butadiene-styrene (ABS) phase is observed when PC/MWCNT masterbatch is diluted with PC and ABS by melt mixing for 5 min with 70% of ABS having relatively high rubber content. The migration is explained by a combination of the morphology evolution, high rubber content and higher affinity of MWCNTs to polybutadiene (PB) than to PC. The high rubber content increases the probability of the contact between MWCNTs and elongated rubber particles during the morphology evolution, most MWCNTs are dragged out of the PC phase to the ABS phase by the surrounding rubber particles because of the better affinity of MWCNTs to PB than to PC. As a result of the selective localization of most MWCNTs in the continuous ABS phase, the resulting ABS/PC/MWCNT composites are conductive. However, with a long mixing time of 60 min, most MWCNTs come back to the PC phase due to the change in the structure of PB chains which decreases the interaction between MWCNTs and rubber particles, resulting in non-conductive materials.