A high pressure and high temperature in-situ X-ray diffraction experiment of MgSiO3 perovskite was conducted using a sintered diamond multianvil apparatus (SDMA8) combined with the synchrotron radiation. The unit cell parameters of the perovskite were measured up to 1095-degrees-C at about 20.5 GPa. The thermal expansion coefficient is 0.8(+/0.8)x10(-5) K-1 at 20.5 GPa and room temperature.