The photochemistry of uranyl(VI)-tributylphosphate (TBP) complex in supercritical carbon dioxide (scCO(2)) was studied in the pressure range of 8-40 MPa and from 289 to 336 K. Deactivation rate constants decreased with the increase of pressure. Temperature dependence analysis of the deactivation rate constants indicated that scCO(2) contributes differently to deactivation processes from liquid phase CO2 based on activation barriers. An UV irradiation experiment proved photochemical reduction of uranyl(VI)-TBP complex by ethanol in scCO(2).