Alumina/reduced graphene oxide composite dispersed aqueous nanofluids with various concentrations have been synthesized successfully by a two-step process: synthesis of Al2O3/rGO composite via solvothermal reaction method and preparation water-based nanofluids through ultrasonication treatment. The crystal phase structure and morphology of the prepared composite have been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The suspension stability and thermal conductivity of as prepared Al2O3/rGO-water nanofluids with different composite concentration have been studied in detail. The overall value of thermal conductivity increases along with increasing concentration at various temperatures, indicating potential application for heat transfer field.