Tungsten oxide nanoparticles have unique optical, electrical, and structural properties and wide variety of applications in chemical and selective catalysis, mechanical sensors, electrochemical industry, and environment [1, 2]. WO3, with the average particle size of 19 nm were prepared by hydrothermal method. The nanoparticles were characterized by X-ray diffraction, transmission electronic microscopy (TEM), High-resolution TEM, and Energy dispersive X-ray spectroscopy. The XRD pattern showed the crystal structural is monoclinic. Nanofluids, as a kind of engineering material are nanoscale colloidal suspensions consisting of nanometer sized solid particles, fibers, rods, or tubes suspended in different base fluids [3].The study of nanofluids is an important branch of nanotechnology since it has potential applications in various areas such as transportation and electronics cooling, biomedicine, and oil drilling [4, 5]. Prepared tungsten oxide nanoparticles were dispersed in ethylene glycol as base fluid by ultrasonic waves. The rheological properties of the nanofluids of tungsten oxide nanoparticles in ethylene glycol were studied as functions of mass fraction, temperature, and shear rate. The resulting nanofluids showed either Newtonian or non -Newtonian behavior depending on their shear rate. The experimental results showed that the viscosity of nanofluid increases with increasing the mass fraction and decreases with increasing temperature as exponentially. References [1] S.K. Deb, Sol. Energ. Mat. Sol. C., 92 (2008) 245. [2] J.S.E.M. Svensson, C.G. Granqvist, Sol. Energ. Mat., 11 (1984) 29. [3] Y. Li, J.E. Zhou, S. Tung, E. Schneider, S. Xi, Powder Technol., 196 (2009) 89. [4] I.M. Mahbubul, R. Saidur, M.A. Amalina, Int. J. Heat Mass Tran., 55 (2012) 874. [5] Y. Rao, Particuology, 8 (2010) 549-555

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