A well-known photochemical process of (UO22+)-O-VI reduction to UVO2+ in the presence of alcohols was studied by density functional theory (DFT) calculations. It was found that the first process which takes place is a photoexcitation of the ground-state UO22+ to the triplet excited state (*UO22+) followed by a significant shortening of the *UO22+-to-alcohol O-ax-H distance. A charge transfer from *UO22+ to alcohol and hydrogen abstraction takes place in the following step. Consequently, (UO22+)-O-VI gets reduced to (UO)-O-V(OH)(2+). The photochemical byproduct RCHOH acts further as a reducing agent toward UO22+ to yield UO2+ and RCHO (aldehyde). Only a combination of these two reactions can explain a high quantum yield of this reaction. In the absence of alcohol, the lowest-lying triplet state exhibits a different character, and photoreduction is unlikely to take place via the same mechanism. The present results agree well with recent experimental finding [J. Am. Chem. Soc. 2006, 128, 14024] and supports the idea that the O-ax-H linkage between UO22+ and the solvent molecule is the key to the photochemical reduction process.