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This study presents the influence of various types of nanoparticle (NP) fillers incorporated into a polyurethane (PU) (VUKOL 022) matrix and its subsequent changes in complex permittivity. Two types of surface modification of SiO₂ fillers were investigated. The frequency dependence of the real and imaginary parts of complex permittivity was measured within the frequency range of 1 mHz to 1 MHz using the capacitance method. The 1 wt.&#x0025; NPs in PU caused an increase (MgO, TiO₂, n-SiO₂, and f-SiO₂) or a decrease (d-SiO₂) in the real permittivity. The <inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>-relaxation and intermediate dipolar effect were observed at the temperature dependence of the imaginary permittivity. The change in permittivity by various surface modifications of SiO₂ and other nanofillers was discussed based on the multi-core model. Moreover, the NPs caused a shift in the local maximum of the permittivity, which was a result of the interfacial polarisation and a charge multiplication of the <inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>-relaxation process.