Nanofluids refers to a new form of heat transfer material that is produced by suspending nanoscale metal and non-metallic particles (1-100 nm) in the base fluid and is one of the newest attempts in the heat sciences. In fact, conventional fluids that are used for heat transfer have a low thermal conductivity. On the other hand, nano particles increase the thermal conductivity coefficient of the fluid due to their high thermal conductivity coefficient with presence in the base fluid. As a result, the vast investment of advanced countries in nanotechnology, research into the thermal properties of nanofluids has been given particular attention. In recent years, nanofluids have attracted the attention of many scientists due to the significant increase in thermal properties. They have been considered as a new approach in heat transfer operations. This paper presents an overview of researches on rheological behavior of nanofluids. This paper examines the effects of parameters such as nanoparticle size and shear rate on rheological behavior of nanofluids. In addition, nanoparticle types and their volume fraction are investigated. It is observed that nanoparticle size, volume fraction and shear rate significantly affect the rheological behavior of the nanofluids. (C) 2018 Elsevier B.V. All rights reserved.