The effects due to temperature and shearing time on viscosity for Al2O3/water and CNT/water based nanofluids at low concentration and low temperatures are experimentally investigated. The viscosity data were collected using a stress-controlled rheometer equipped with parallel plate geometry under up and down shear stress ramp. CNT and Al2O3 water based nanofluids exhibited hysteresis behaviour when the stress is gradually loaded and unloaded, depending also on shearing time. Experiments also showed that the nanofluid suspensions indicated either Newtonian or non-Newtonian behaviour, depending on shear rate. CNT water based nanofluid behaves as Newtonian fluid at high shear rate whereas Al2O3 water based nanofluid is non-Newtonian within the range of low temperatures investigated. (C) 2012 Elsevier Ltd. All rights reserved.