During Earth s accretion, Earth s mantle is expected to have been a magma ocean due to large impacts. As such, properties of molten mantle materials are key to understanding Earth s thermochemical evolution. However, due to experimental challenges, transport properties at lower mantle pressures, particularly viscosity, are poorly constrained for mantle melts. In this study, we use quenched dendritic textures to estimate melt viscosities at high pressures for (Mg, Fe)O ferropericlase, one of the major components of the mantle. We find that the viscosity of (Mg, Fe)O melt near liquidus temperatures is 10−3–10−2 Pa s over the pressure range of 3–70 GPa, which is 1–2 orders of magnitude lower than previous results for Si-rich melts at similar conditions. This may have implications for magma ocean cooling and thermochemical evolution of the mantle. ©2017. American Geophysical Union. All Rights Reserved.