The highly photosensitive characteristic of poly-sulfide chetomins was first unveiled, and four new unstable analogues, chetomins A-D (1-4), with significant cytotoxicity were successfully purified in darkness. The visible-light-induced desulfurization and intermolecular disproportionation were revealed to initiate the interconversion of chetomin analogues, which explained the long-recognized puzzle of rarity and instability of chetomin analogues.