Abstract: Studies of the structure-property relationship of multicomponent polymer/inorganic fillers systems have gained in a great interest in the development of high performance microwave shielding materials. Herein, a simple strategy of improving the electromagnetic interference (EMI) shielding effectiveness of composites was to distribute nanofillers in different phases of a blend structure. This was accomplished by designing a ternary blend with core-shell structure using poly(vinylidene fluoride) (PVDF), poly(styrene) (PS), and high-density poly(ethylene) (HDPE). Here, HDPE phase was the core and PS phase was the shell. When multiwalled carbon nanotubes (MWCNTs) was added into PVDF/PS/HDPE blends, it stably dispersed in the PS shell layer. In addition, the magnetic properties of the blends were tuned by controlling the Fe3O4 nanofillers localization under macroscopic processing condition. The attenuation of electromagnetic (EM) radiation was analyzed by evaluating the total shielding effectiveness (SET) in X band. The absorption of the incoming microwave radiation has been improved due to the synergetic effect from MWCNTs and Fe3O4. Thus this study opened a new avenue in designing the composites for building block of electromagnetic shielding applications.