A structure refinement of MgSiO3 with the ilmenite-type structure has been carried out with single crystal X-ray diffraction techniques. Magnesium and silicon atoms are completely ordered in the structure. The magnesium silicates with higher transition pressures have smaller MgO6 and larger SiO6 octahedra than those with lower transition pressures, resulting in more compact arrangements of oxygen atoms in the higher-pressure phases. Cation-oxygen distances of ilmenite-type structures systematically change depending on the ionic radii of cations, and this relation is followed for Mg-o and Si-o distances of ilmenite-type MgSiO3. The degree of distortion of cation octahedra in the ilmenite-type structures is independent of the kinds of cations but the shifts of cations from the centers of octahedra systematically change as a function of ionic radius.