Oil-in-water microemulsion of all-trans retinene (ATRN) was synthesized in which SDS was used as surfactant, 1-butanol as cosurfactant, and cyclohexane as oil phase. Then 355 nm laser flash photolysis was used to investigate the transient photochemistry of ATRN in the microemulsion. The results showed that ATRN can be photoexcited by 355 nm laser light to produce the triplet state of ATRN (3ATRN*) with λmax ≈ 470 nm. In acidic solution, 3ATRN* can react with diphenylamine (DPA) via electron transfer to produce transient products of ATRN neutral radical and DPA radical cation. The study on the reactivity of 3ATRN* with lysozyme, amino acids and antioxidants showed that 3ATRN* may not interact directly with biomolecules, and ATRN may be phototoxic via PDT Type II photosensitization process.Cited