As determined from powder X-ray diffraction experiments with synchrotron radiation, the thermal expansion coefficient of forsterite increases smoothly from 2.8 to 4.5 K-1 from 400 K to 2160 K. No anomalous increases of the cell parameters are observed near the melting point. The consistency between the observed and calculated value of the initial slope of the melting curve of forsterite suggests that defects do not make a large contribution to thermal expansion near the melting point. Along with previous results, the new data confirm the influence of anharmonicity on the high-temperature heat capacity of forsterite and indicate that both the Gr¿neisen parameter and &agr;KT (&agr;=thermal expansion coefficient, KT=bulk modulus) have nearly constant values at high temperatures. ¿ American Geophysical Union 1996