Plate heat exchangers (PHEs) are utilized in heating or cooling processes in many applications like power plants, manufacturing and food industries. The thermophysical properties of the working fluids used in PHEs are a major factor in efficiency. The purpose of utilizing nanofluid as the working fluid in PHEs is to gain maximum heat transfer rate by changing the weak thermophysical specifications of the conventional fluid. In this study, heat transfer characteristics of Fe2O3/water and Fe3O4/water nanofluids have been measured in a PHE empirically. The weight concentrations of 0.5 and 1% of both Fe2O3/water and Fe3O4/water nanofluids have been investigated at four various Reynolds numbers. For best dispersion of nanoparticles in the main fluid, the surfactant Triton X-100 has been added into the solutions at 0.05% weight concentration. The performance tests have been done at different outlet temperatures including 40°C, 45°C, 50°C, and 55°C. Experimental findings demonstrated that utilizing nanofluids raised the thermal effectiveness of the PHE notably. Moreover, increasing nanofluid ratio and Reynolds number enhanced heat transfer rate and the overall heat transfer coefficient. In addition, when the two nanofluids have been compared, the Fe3O4/water nanofluid has priority at equal particle ratios. The highest improvement in overall heat transfer coefficient, heat transfer rate, and effectiveness were obtained as 19.2%, 19%, and 11.5% by utilizing Fe3O4/water nanofluid with weight concentration of 1%. © 2022 by Begell House, Inc.