Abstract: Photoisomerization of isosafrole has been studied. Direct irradiation or triplet sen-sitization results in cis-trans isomerization and the stationary states become richer in cis-isosafrole. When 9,10-dicyanoanthraeene, 9-cyanoanthracene and chloranil are used as sensitizer, electron transfer photoisomerization takes place and the stationary states become richer in the trans-isomer. The reactants and products are identified by GC-MS, IR and NMR. A tentative mechanism for the photoisomerization is proposed.