Nanofluid is a novel heat transfer fluid prepared by dispersing nanometer-sized solid particles in traditional heat transfer fluid to increase thermal conductivity and heat transfer performance. In this research we have considered the rheological properties of nanofluids made of CuO particles of 10-30nm in length and ethylene glycol in conjunction with the thermal conductivity enhancement. When examined using TEM, individual CuO particles have the shape of prolate spheroid of the aspect ratio of 3 and most of the particles are under aggregated states even after sonication for a prolonged period. From the rheological property it has been found that the volume fraction at the dilute limit is 0.002, which is much smaller than the value based on the shape and size of individual particles due to aggregation of particles. At the semi-dilute regime, the zero shear viscosity follows the Doi-Edwards theory on rodlike particles. The thermal conductivity measurement shows that substantial enhancement in thermal conductivity with respect to particle concentration is attainable only when particle concentration is below the dilute limit.