The gas-phase hydrolyses of CF3COF catalyzed by water have been theoretically investigated at the CBS-QB3 level, in which up to four water molecules are considered explicitly and the effect of water bulk solvent is also considered within the polarizable continuum model (PCM). Both stepwise and concerted pathways are identified for hydrolyses of CF3COF, which are competitive with the increasing number of the water molecules. The activation Gibbs free energies are decreased from about 40 kcal mol(-1) to 20 kcal mol(-1) due to the catalytic effect of water molecules.