One of the new methods for improving heat transfer in thermal systems is the use of nanofluids. In this research, the laboratory process of preparation, the stability and measurement of the thermal conductivity of a new hybrid nanofluid were performed. The hybrid nanofluid was prepared by suspending a combination of copper oxide and graphene oxide in antifreeze. At first, the characterization of nanoparticles was performed to investigate the surface and atomic structure of the nano-materials using XRD & FESEM tests. The nanofluid was produced by a two-step method, and its stability was investigated using both sedimentation mapping and DLS testing. The DLS results showed the samples had a nano structure. The measurement of the thermal conductivity of the hybrid nanofluid was carried out using a KD2-Pro thermal analyzer and a KS-1 sensor in a temperature range of 25-50 degrees C with volume concentration range of 0-1.6%. The results of the experiments showed that the thermal conductivity of the nanofluid is a function of volume fraction and temperature. Moreover, the effects of temperature on thermal conductivity were more evident in more concentrated samples. It was also observed that the thermal conductivity of the nanofluid increased by 43.4%. In the end, using a curve fit method and based on experimental results, an experimental correlation with high precision was presented to predict the thermal conductivity of hybrid nanofluid. Therefore, according to the results, it was understood that this nano-antifreeze could be used as an alternative fluid with high heat transfer potential in thermal systems. (C) 2019 Elsevier B.V. All rights reserved.