Multiwalled carbon nanotubes (MWCNTs) can endow high dielectric constant to polymer-based composites. However, the accompanying poor dispersion of MWCNTs and high dielectric loss for composites severely limit their application in dielectric field. Herein, a modified acid-treated MWCNTs encapsulated by the polyaniline/poly(sodium 4-styrenesulfonate) layers (aMWCNTs@PANI-PSS) with a one core-two shell structure was fabricated by in situ polymerization followed by electrostatic self-assembly technique. Furthermore, the composite films based on aMWCNTs@PANI-PSS/poly(vinylidenefluoride-hexaflouropropylene) (PVDF-HFP) were fabricated by a solution-casting method. An ultrathin insulating PSS shell is wrapped onto aMWCNTs@PANI, resulting in the improvement of dispersibility for aMWCNTs@PANI and the decrease of dielectric loss for composite films. When the content of aMWCNTs@PANI-PSS is 5.0 wt %, the dielectric constant of aMWCNTs@PANI-PSS/PVDF-HFP reaches 430 (100 Hz), which is about 55 times of pure PVDF-HFP and 1.7 times of aMWCNTs@PANI/PVDF-HFP (247). Besides, the responding dielectric loss of aMWCNTs@PANI-PSS/PVDF-HFP composite film is only 0.67, much lower than that of aMWCNTs@PANI/PVDF-HFP (25) and aMWCNTs/PVDF-HFP (3185). (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 948-956