In this work, Polyvinylidene Fluoride (PVDF)/polystyrene (PS)/high density polyethylene (HDPE) ternary blends displayed a core-shell structure where HDPE was the core, PS was the shell, and this core-shell system dispersed in PVDF matrix. Here, multiwall carbon nanotubes (MWCNTs) and ferroferric oxide (Fe3O4) was incorporated. F-F composites with MWCNTs was in PS shell and Fe3O4 was in PVDF matrix and E-F composites with MWCNTs was in PS shell and Fe3O4 was in HDPE core were fabricated by melt blending. It was indicated that the core-shell morphology between PS and HDPE was well retained with the incorporation of Fe3O4 and MWCNTs. Both the electrical conductivity of F-F and E-F composites were similar without no obvious change with the incorporation of Fe3O4. Composites with greater than 20 dB shielding effectiveness were easy to obtain. The highest SE we observed was for the F-F composite with 1 vol% Fe3O4 and 1 vol% MWCNTs was 25 dB at 9.5 GHz, and the SE was over 20 dB in the whole measured frequency(X-band). The E-F composites with SE greater than 20 dB in X-band was at 2 vol% Fe3O4 and 1 vol% MWNCTs. Such effective and lightweight nanocomposites were obtained, resulting from the synergetic effect of MWCNTs and Fe3O4 nanoparticles. (c) 2018 Elsevier B. V. All rights reserved.