To improve the understanding of large-scale planetary processes, i.e. differentiation and core formation, of Earth and other planetary bodies, we performed experiments at 1 GPa in a range of 2 temperatures to investigate mass-dependent isotope fractionation of ruthenium (Ru) between metal, silicate, and sulfide melts. Metal silicate fractionation is Ru/ 99 Rusilicate-102 Ru/ 99 Rumetal = 0.02 ± 0.02 ‰ (95% confidence interval) at °C and therefore negligible for Earth's core formation. However, there is resolvable Ru isotope fractionation between liquid metal and liquid sulfide: The 102 Ru/ 99 Ru ratio of liquid sulfide is 0.11 ± 0.03 ‰ lighter than that of liquid metal at 1400 °C in sulfur (S)-bearing experiments. The unexpected lighter Ru isotope composition of the sulfide can be best explained with different Ru-S bonding environments. Our results show furthermore, that addition of tin (Sn) instead of S to experimental charges affects Ru isotope fractionation significantly. The 102 Ru/ 99 Ru ratios in the Sn-bearing phase are 0.18 ‰ ± 0.01 ‰ heavier than metal; hence, the presence of Sn not only changes the magnitude of the Ru isotope fractionation but also its direction. The observed Ru isotope fractionations are too small to preserve a resolvable isotope fractionation signature during core formation or the Hadean matte scenario at very high temperatures.