The new rearranged diterpenoid (1)* and the flavonoids, centaureidin (9) and quercetagetin 3,6-dimethyl ether (10), have been isolated from an extract of Olearia muelleri (Sond.) Benth. Centaureidin has a weak cytotoxic action in an anti-tumor assay system, accounting, in part, for bioactivity of the plant extract.