The elastic constants of UO2 have been measured as a function of pressure up to 20 kbar (2.0 GPa) at 23 °C. To within experimental uncertainty, the constants are linear functions of pressure, and no pressure‐induced phase transitions occur in this 20‐kbar pressure range. The elastic constant data are used to estimate the various polycrystalline elastic moduli and their pressure dependences, and the zero‐pressure moduli are compared with data from polycrystalline material. Isothermal moduli are calculated from the adiabatic values. The elastic‐constant data are also used to discuss the separation of the ’’pure’’ volume and temperature contributions to the (isobaric) temperature dependences of the elastic constants as well as to estimate the Grüneisen constant, Debye temperature, and equation of state of this material.