(all-E)-5,6-Diepikarpoxanthin (=(all-E,3S,5S,6S,3'R)-5,6-dihydro-beta,beta-cirotene-3,5,6.3'-tetrol; 1) was submitted to thermal isomerization and I-2-catalyzed photoisomerization. The structures of the main products, i.e. (9Z)- (2) (9'Z)- (3), (13Z)- (4), (13'Z)- (5), and (15Z)-5,6-diepikarpoxanthin (6), were determined by their UV/VIS, CD, H-1-NMR, and mass spectra. In addition, (9Z,13'Z)- or (13Z,9'Z)- (7), (9Z,9'Z)- (8), and (9Z,13Z)- or (9'Z,13'Z)-5,6-diepikarpoxanthin (9) were tentatively identified as minor products of the I-2 catalyzed photoisomerization.