A major polyacetylene compound from Panax ginseng roots, heptadeca-1-en-4,6-diyn-3,9,10-triol, was irradiated with 300 nm UV light to obtain a photooxidized acetylenic compound having the conjugated en-on-diyne chromophore, heptadeca-1-en-4,6-diyn-9,10-diol-3-one. The same oxidation product was obtained exclusively by 4-(dimethylamino) pyridinium chlorochromate at room temperature.