The mechanism for the extraction of V, when effected by the photochemical reduction of V(V) to V(IV), was investigated, employing bis(2-ethylhexyl)phosphoric acid as the extractant, n-dodecane as the diluent, and a xenon lamp as the ;ight source. The photochemical reduction of V(V) progresses at a rate that is first order with respect to the concentration of V(V) in both aqueous and organic solutions. Reduction also occurs, in the extraction system, at the interface between the aqueous and organic phases. The observed time-course variation in the distribution ratio with respect to photoirradiation is expressed successfully by a proposed scheme, in which the photochemical reduction of V(V) is a rate-determining step. The organic solution obtained following photoirradiation can be reused for repeated photoreductive extraction-stripping processing.