High pressure phase relations of MgSiO3 and Mg2SiO4 have been studied up to pressures higher than 300 kbar, using a double-stage split-sphere apparatus. It has been confirmed that the ilmenite phase of MgSiO3 and &ggr;-Mg2SiO4 transform directly at about 300 kbar to the orthorhombic perovskite phase and the assemblage of MgSiO3 perovskite plus MgO periclase, respectively. These results are consistent with those by Liu [1976 a and b> but do not support the stability of oxide mixture (periclase plus stishovite) claimed by Kumazawa et al. [1974> and Ming and Bassett [1975 a and b>.