Experimental investigations are performed in order to determine the thermal conductivity of NiFe2O4 nanoparticles dispersed in deionized water. The magnetic nanoparticles are synthesized using a microemulsion method. The X-ray diffraction (XRD), transmission electronic microscopy (TEM), and vibration sample magnetometer (VSM) are used to characterize the structure, the size and the magnetic properties of the nanoparticles. The VSM results disclose that the NiFe2O4 nanoparticles are ferromagnetic at room temperature. Experimental measurements on thermal conductivity of the prepared nanofluids are conducted at different volume concentrations between 0% and 2% and in the temperature range of 25-55 degrees C. The experimental results show that the thermal conductivity of nanofluids increase with an increase in volume concentration and temperature. The Maximum enhancement in thermal conductivity of nanofluids is 17.2% at 2% volume concentration and in temperature of 55 degrees C. Finally, the experimental results of thermal conductivity are fitted with a new correlation to predict the thermal conductivity of nanofluids. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.