Capillin is a toxic naturally occurring organic compound with the chemical formula . The structure contains acetophenone and a polyyne (pentadiynyl) portion, conjugated together as an ynone.
Capillin is found in the essential oil of a number of Artemisia species, including Artemisia monosperma and Artemisia dracunculus (tarragon). The substance was initially isolated from Artemisia capillaris in 1956.
Capillin is a biologically active substance. It has strong antifungal activity, and it is possibly antitumoral. Capillin exhibits cytotoxic activity and could cause apoptosis of certain human tumor cells.