Nanofluids are solid-liquid dispersions containing nanoparticles of size 1-100 nm in a liquid. Nanofluids that have enhanced thermal conductivity are best known for their application as coolants in food storage, transportation, refrigeration and air-conditioning industries. Considerable energy savings can be realized through the use of nanofluids as coolants. Viscosity is one of the major transport properties that determine the heat removal capability of nanofluids. The present study reports the effect of calcination temperature on the primary particle size, aggregate size of the ZnO nanoparticles and on the transport properties of the ZnO-water nanofluid. ZnO nanoparticles have been synthesized using Zinc nitrate hexahydrate as precursor. The primary particle size of the ZnO nanoparticles calcined at different temperatures ranging from 100-500°C was found to be in the range of 40-60 nm. The effect of calcination temperature on hydrodynamic size distribution of the ZnO nanoparticles has been investigated using dynamic light scattering technique. The viscosity of ZnO-water nanofluids, using ZnO powders prepared at different calcination temperatures have also been studied, along with their colloidal stability. [ABSTRACT FROM AUTHOR]