Aqueous nanofluids composed of alumina nanoparticles with different sizes at a concentration from 0.1vol% to 0.5vol% were prepared by a two-step method. The suspension and dispersion characteristics were experimentally examined by zeta potential, average size and absorption spectrum. The thermophysical properties such as the viscosity, surface tension, thermal conductivity, saturation vapor pressure and latent heat of vaporization were measured. The influences of the particle size, particle volume concentration and temperature on the thermophysical property were investigated. It was found that the viscosity and thermal conductivity increased with decreasing nanoparticle size. In contrast, the surface tension, saturation vapor pressure and latent heat of vaporization decrease with decreasing nanoparticle size. The viscosity, thermal conductivity and saturation vapor pressure have an increasing tendency with increasing volume concentration. However, surface tension and latent heat of vaporization showed a reverse tendency. Furthermore, the temperature also showed had obvious influence on the nanofluids viscosity, thermal conductivity and surface tension.