Eucalyptol is a natural organic compound which is a colorless liquid. It is a cyclic ether and a monoterpenoid.

Eucalyptol is also known by a variety of synonyms: 1,8-cineol, 1,8-cineole, limonene oxide, cajeputol, 1,8-epoxy-p-menthane, 1,8-oxido-p-menthane, eucalyptol, eucalyptole, 1,3,3-trimethyl-2-oxabicyclo[2,2,2]octane, cineol, cineole.

Eucalyptol has a fresh camphor-like smell and a spicy, cooling taste. It is insoluble in water, but miscible with ether, ethanol and chloroform. The boiling point is 176 °C and the flash point is 49 °C.

Eucalyptol comprises up to 90 percent of the essential oil of some species of the generic product Eucalyptus oil, hence the common name of the compound. It is also found in camphor laurel, bay leaves, tea tree, mugwort, sweet basil, wormwood, rosemary, sage and other aromatic plant foliage. Eucalyptol with a purity from 99.6 to 99.8 percent can be obtained in large quantities by fractional distillation of eucalyptus oil.

Although it can be used internally as a flavoring and medicine ingredient at very low doses, typical of many essential oils (volatile oils), eucalyptol is toxic if ingested at higher than normal doses.

Eucalyptol is an ingredient in many brands of mouthwash and cough suppressant. It controls airway mucus hypersecretion and asthma via anti-inflammatory cytokine inhibition. Eucalyptol is an effective treatment for nonpurulent rhinosinusitis. Research showed that treated subjects experienced less headache on bending, frontal headache, sensitivity of pressure points of trigeminal nerve, impairment of general condition, nasal obstruction, and rhinological secretion. Side effects from treatment were minimal. Eucalyptol reduces inflammation and pain when applied topically. It kills leukaemia cells in vitro.

Eucalyptol is used as an insecticide and insect repellent. Conversely, eucalyptol is one of many compounds that is attractive to males of various species of orchid bees, who apparently gather the chemical to synthesize pheromones; it is commonly used as bait to attract and collect these bees for study.