We describe an approach to tailor the dielectric interfacial properties of polymer blends by the interplay of compatibilizer effects on blend morphology and on blocking of charge carriers. A systematic study of the effect of the concentration of the compatibilizer, a random copolymer of poly(styrene-random-methyl methacrylate) (PS-r-PMMA), on the interfacial properties of stacked polymer films and a phase separating blend of poly[(α-methylstyrene)-co-acrylonitrile]/poly(methyl methacrylate) (PαMSAN/PMMA) was performed. From dielectric spectroscopy, "conductivity free" dielectric loss spectra revealed interfacial blocking of charge carriers at low frequencies owing to the conductivity contrast of the blend components, resulting in a dielectric interfacial peak. From the dielectric response of stacked polymer films, the interfacial polarization was significantly suppressed when the thickness of the more conducting film approached the Debye length (LD), on the basis of which LD could be calculated using the Trukhan model. With increasing concentration of interfacially localized copolymer, an increase of the relaxation strength of the interfacial polarization occurred due to a pronounced decrease of LD. The characteristics of the former were further investigated in biphasic polymer blends and were governed by the intrinsic length scale of the system, i.e., the ratio of structure dimension (Dv) to Debye length (LD). Upon compatibilization, the interfacially segregated copolymer not only results in refinement of the PαMSAN phase but also provides an augmented conductivity difference leading to a slower dynamics of PαMSAN charges at the interface. This resulted in a substantial increase of the peak intensity of the interfacial polarization, which was attributed to a pronounced attenuation of LD. The latter parameter was estimated using either the impedance formalism or the interfacial relaxation time. Similar to the stacked polymer films, upon compatibilization, an increase of the relaxation strength of the interfacial polarization occurred in biphasic polymer blends, which corroborated a pronounced decrease of LD. Our results provide a methodology to characterize and tune the morphology and blocking of charge carriers with the aim of tailoring the dielectric interfacial properties of biphasic morphologies.