In an effort to shed light into the role of surface morphology of nanopartides on their thermal properties, we have prepared Fe3O4 and CuO nanoparticles of different sizes and morphologies using co-precipitation and precipitation approach, respectively. The prepared particles are characterized using Small Angle X-ray Scattering (SAXS) and the results are compared with X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and Dynamic Light Scattering (DLS). The results show that the size distribution and surface morphologies of nanoparticles can be quite accurately measured by using SAXS with the aid of appropriate models. The thermal conductivity of spherical Fe3O4 nanofluids follows effective medium theory whereas the CuO nanorod based dispersions show a much larger thermal conductivity beyond the effective medium theory. The abnormal thermal conductivity in CuO is attributed to effective conduction of heat through nanorods of higher aspect ratio. These finding are useful for engineering efficient nanofluids for thermal management. (C) 2014 Elsevier B.V. All rights reserved.