This study investigates the rheological behavior of fumed silica nanoparticle suspended in polyethylene glycol (PEG) at steady and oscillatory shear stress using a stress controlled rheometer. The suspension was prepared at different concentration from 25 to 45 wt.% silica nanoparticle and studied under the temperature of 20-60 degrees C. It is found that the fumed silica/PEG suspension exhibits shear-thickening behavior. Effects of silica nanoparticle concentration and solution temperature on the rheological behavior of silica suspensions in terms of initial viscosity, critical viscosity, and peak viscosity were quantitatively studied through the response surface method (RSM). The individual and interaction effects of silica concentration and temperature on viscosity of suspensions showed significant increase of critical viscosity versus silica concentration. On the contrary, a montonic decrease was observed as a function of solution temperature. Moreover, it is found that the onset of shear thickening for the sample with high silica content appeared at lower shear rate. Furthermore, increasing the temperature of suspension leads to an increasing the critical shear rate. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.