The thermal expansivity of PtC with the rock-salt and zinc-blende structures under high pressures and temperatures are predicted by using first-principles density functional theory calculations combined with the quasi-harmonic Debye model. The effects of the pressures and temperatures on the P-V-T relationship and the volume thermal expansion coefficient a are successfully investigated for both two structures. It is found that the alpha increases with temperature at all pressures for zinc-blende phase and it is a weak function of temperature at high temperatures for rock-salt phase. The properties of cubic PtC are summarized in the pressure range of 0-100 GPa and the temperature up to 3000 K. (C) 2011 Elsevier B.V. All rights reserved.