Two decades have been going on since nanofluid was introduced with the hope that it could enhance the thermal performances of heat transfer applications. Nevertheless, yet, there are no standards for nanofluid preparation process (sonicator type, power, amplitude, duration) to achieve stable and well-dispersed nanofluid. The aim of this research is to analyze the consequence of ultrasonication duration on colloidal dispersion and thermophysical properties of 0.5 vol.% of Al2O3-water nanofluid. A horn ultrasonic dismembrator was used for different periods from Oh to 5 h for nanofluid preparation. Particle size distribution (PSD), zeta potential, and microstructure were studied to check the dispersion characteristics. Thermal conductivity, viscosity, and density of the nanofluid were analyzed for different temperatures from 10 degrees C to 50 degrees C. Better dispersion, higher thermal conductivity and density, and lower viscosity have been observed with the increase of sonication time. Furthermore, thermal conductivity was found to be increased but viscosity and density were decreased with the increase of temperature. The research concluded that higher ultrasonication duration is best and at least 2 h of ultrasonication is needed for better performance of the nanofluid. (C) 2015 Elsevier Ltd. All rights reserved.