We provide rheological and dynamic insights into the role of an in situ reactive interphase with graft copolymers in multilayered polymer systems, using a polyamide-6 (PA6)/maleic anhydride grafted poly(vinylidene fluoride) (PVDF-g-MAH) bilayer as a model. Firstly, the influence of the reactive interphase on macroscopic melt flow behavior was studied. The in situ generated interphase from coupling reactions in bilayers significantly contributed to overall viscoelastic responses in both linear and nonlinear regimes. Specifically, under fast extensional flows, the reactively healed bilayer showed enhanced strain hardening mainly due to the formed graft copolymers in the interphase. Secondly, the evolution of a reactive interphase and its effects on microscopic dynamics and structural properties were further probed using dielectric relaxation spectroscopy (DRS). Interestingly, the reactive interphase drastically altered the dielectric responses of the bilayer upon healing, manifesting in the distinct interfacial relaxation/polarization. The relaxation strength of the interfacial polarization increased linearly as a function of reaction time, and was further improved by increasing the number of layers. In agreement with the rheology, DRS also demonstrated the retarded microscopic dynamics of a reactive interphase in healed bilayers. Using the dielectric molecular relaxation spectrum as a probe for the structure, the effects of the reactive interphase on charge dynamics and the resulting structural properties of bilayers were further evaluated. These findings are aimed at providing a better understanding of the effects of the reactive interphase on rheology, dynamics and dielectric properties, towards controlling the interface/interphase in multi micro-/nano-layered polymer structures and for further applications.