Stable Fe3O4-water nanofluids are prepared and sedimentation observation is used to investigate its stability. A convection heat transfer experiment is set up to investigate the thermo-hydraulic performances of Fe3O4-H2O nanofluids in a circular tube considering the effects of different nanoparticle mass fractions (omega = 1.0%, 3.0% and 5.0%), Reynolds Numbers (Re = 600-11000) and paralleled magnetic induction intensities (B = OG, 100G, 200G and 300G). The result is that Nusselt number is proportional to nanoparticle mass fraction but opposite trend is found with the increasing paralleled magnetic induction intensity. Nanofluids with omega = 5.0% show the best performance of heat transfer. The resistance coefficient increases with mass fraction and can be enhanced by magnetic field further. Nanofluids with omega = 5.0% under magnetic induction intensity B = 300G show the largest resistance coefficient. A comprehensive evaluation index and an exergy efficiency evaluation plot are developed to discuss the thermo-hydraulic performances of nanofluids from quantity and quality. The thermo-hydraulic performance increases with nanoparticle mass fraction but decreases with paralleled magnetic induction intensity. (C) 2019 Elsevier Ltd. All rights reserved.