In this study, the pool boiling heat transfer coefficient in the nucleate regime was investigated by a pool boiling device using nickel oxide nanoparticles in the base-fluid of deionized water, in the presence of magnetic fields. The heat transfer coefficient was obtained by the measured temperatures and the heat transfer equations. The experimented concentrations include 0.005, 0.001, 0.05, 0.1, and 02, volumetric concentrations. Tests, including Transmission electron microscopy (TEM), Dynamic light scattering (DLS), X-ray diffraction (XRD), and Zeta Potential, were utilized for validation of the particle sizes and the stability of the nanofluid. The size of the particles was measured to be 10-60 nm. The results indicated that the highest increase of the heat transfer coefficient was for the 0.005 concentration, compared to the deionized water. The Gauss values in the magnetic fields of 50,100, 200, and 300 were shown to be 27.3, 30.8, 352, and 37.5, respectively. Also, the results have demonstrated that increasing the intensity of the magnetic field may have a positive effect on the heat transfer enhancement. However, in higher concentrations, a negative effect on the heat transfer enhancement was observed. (C) 2020 Elsevier B.V. All rights reserved.