Deselenization of 1,2-diselenides offers a promising tool for the construction of organochalcogenides. However, the requirement of transition metals and harsh reaction conditions are still significant challenges in this transformation. Herein, we have developed a metal-free and catalyst-free photocatalytic system for deselenization of 1,2-diselenides with PCy₃, providing convenient access to monoselenides under mild conditions. Most importantly, the visible-light-induced protocol allowed for the deselenizative cross-coupling reaction between two different diselenides as well as the deselenizative cross-coupling reaction between a diselenide and a disulfide to provide unsymmetrical monoselenides and sulfides, respectively. DFT computational studies demonstrated that the chemoselectivity in the deselenizative cross-coupling reaction is derived from the difference in the C–Se bond dissociation energies as well as the polarity-matching effect. Mechanistic studies disclosed that the key to the deselenization lies in the generation of carbon-centered radicals through sequential Se–Se bond and C–Se bond cleavage of 1,2-diselenides.