Acetylacetone (acac) ligand has been used for stabilization of ZnO NPs in water that form weak chelating complex which simultaneously breaks ZnO clusters, wrap and make ZnO NPs water soluble. Both thermal effusivity and conductivity show sigmoidal behavior over a temperature range of 283323 K for low concentration fluids. The flow characteristics show rheopectic behavior according to concentration of ZnO NPs with highly non-Newtonian characteristics at lower shear stresses. Temperature dependence of the rheological characteristics suggests that above room temperature viscosity is higher for higher concentration nanofluid that can be attributed to agglomeration. (C) 2010 Elsevier B.V. All rights reserved.