Chemical reaction between liquid iron and (Mg,Fe)SiO3 perovskite was investigated by a combination of laser-heated diamond anvil cell (LHDAC) and analytical transmission electron microscope (TEM). The compositions of quenched liquid iron in contact with perovskite were determined quantitatively using both energy-dispersive (EDS) and electron energy loss (EELS) spectra. Results demonstrate that the dissolution both of O and Si into molten iron is significantly enhanced with increasing pressure. The quenched liquid iron contains 5.3 wt% O and 2.8 wt% Si at 97 GPa and 3150 K that can account for the 7% core density deficit. Reaction products such as SiO2, FeSi, and FeO were not observed as stable phases in this study. The bottom of the mantle in contact with outer core liquid could be depleted in iron. O and Si are important light elements in the core, whose contents may have increased over the geological time.