The composite of multiwalled carbon nanotubes (MV/CNTs) decorated with ZrO2 nanoparticles, synthesized by a grafting method followed by high-temperature annealing, was studied. The oxygen functionalized MWCNT surface uniformly disperses and stabilizes the oxide nanoparticles to an extent that is controlled by the metal oxide loading and thermal annealing temperature. This ZrO2/MWCNT also withstands decomposition in a hydrothermal environment providing potential applications in the catalysis of biomass conversion (e.g., aqueous phase reforming). The ZrO2/MWCNT have been characterized by (scanning) transmission electron microscopy ((S)TEM), X-ray diffraction (XRD), in situ small-angle X-ray scattering (SAXS), in situ wide-angle X-ray scattering (WAXS), and near edge X-ray fine structure (NEXAFS) for the purpose of a comprehensive analysis of the ZrO2 particle size and particle size stability.