Abstract. This review paper deals with the nanofluids theoretical thermal conductivity models published by different research groups. It also covers the contrary opinion on anomalous thermal conductivity of nanofluids suggested by different research groups and lists out the nanofluid thermal conductivity models. Numerous works have been carried out on nanofluids and reported the nanofluids have higher thermal conductivity than that of the traditional fluids. In general, the nanofluid theoretical thermal conductivity models have been derived from the classical nanofluid thermal conductivity models. Many research groups proposed the random motion of nanoparticles is the reason for improved thermal conductivity of nanofluids. The thermal conductivity model based on Brownian models is being widely applied in the field of nanofluids application. Though many nanofluids thermal conductivity models have been formulated, there are still some controversial issues covering the inconsistent thermal conductivity data, the sufficiency and suitability of classical nanofluid thermal conductivity models. The nanofluid inconsistencies among the models may be due to the assumption made, depending factors such as particle size, shape, volume fraction, temperature, static, and dynamic conditions of nanoparticles in developing the thermal conductivity models. This review leads to some directions for future research in nanofluids and to help researchers in resolving the controversial issues.