<p>Graphene oxide (GO) and its surface-functionalized derivatives provide a promising platform for tailoring dielectric relaxation and thermal transport through chemical modification. However, a unified understanding of how surface chemistry governs these properties remains limited. In this work, GO, acid-functionalized GO (A-GO), and amine-functionalized GO (N-GO) were synthesized to systematically elucidate the influence of surface functionalization on frequency and temperature-dependent dielectric properties and thermal behavior. Structural and spectroscopic analyses confirmed successful incorporation of –COOH and –NH₂ groups, accompanied by reduced interlayer spacing, modified defect density, and distinct variations in nanoscale sheet morphology and lateral size distribution upon functionalization. Dielectric spectroscopy performed over a frequency range of 10^–2–10⁵ Hz and a temperature range of 25–100 °C revealed thermally activated, non-Debye relaxation dominated by interfacial polarization, with N-GO exhibiting significantly enhanced capacitance (~ 10^–3 F), dielectric permittivity (~ 10⁹), and AC conductivity (~ 10^–1 S m⁻¹) at 100 °C compared with GO and A-GO. Dielectric modulus analysis and impedance spectroscopy were additionally employed to further assess relaxation behavior and charge transport characteristics of the functionalized GO systems. Thermal conduction measurements of corresponding nanofluids demonstrated pronounced enhancement in thermal conductivity and diffusivity with increasing temperature and nanoparticle concentration, reaching up to ~ 71% thermal conductivity enhancement for N-GO nanofluids relative to the base fluid. This work provides the first comprehensive and systematic experimental investigation integrating dielectric relaxation analysis and thermal transport evaluation in acid and amine functionalized GO, offering new insights into the role of surface chemistry in governing multifunctional material performance.</p>