Abstract Four new briarane-related diterpenoids, designated as briaexcavatins C–F ( 1 – 4 ), were isolated from the Formosan octocoral Briareum excavatum , collected off southern Taiwan coast. The structures of these new metabolites were elucidated by the interpretation of spectroscopic and chemical methods. The configuration of 1 was further supported by molecular mechanics calculations. Briarane 1 has been shown to exhibit mild cytotoxicity toward MDA-MB-231 human breast tumor cells and briarane 3 was found to show activity to inhibit neutrophil elastase release in humans.