Abstract The leaf oils of the two Australian species of Decaspermum have been examined by GC and GC/MS. The leaf oil of D. struckoilicum contained α-pinene (37.5%) as its principal component in an oil that contained similar amounts of mono- and sesquiterpenes. The major sesquiterpenes identified in the oil were β-caryophyllene (2.4%), α-humulene (2.2%) and α- and β-eudesmol (8.2% and 8.1%, respectively). Decaspermum humile produced a leaf oil that contained either approximately equal amounts of mono- and sesquiterpenes or had a majority of the latter components. The principal monoterpenes were a-thujene (0.1â13%) and α-pinene (0.2â21%). Other prominent monoterpenes identified were limonene (0.2â8%), myrcene (0.3â10%), β-phellandrene (0.1â5%), linalool (0.3â9%) and terpinen-4-ol (0.3â6%). 1,8-Cineole was usually absent from the oils. The main sesquiterpenes identified in the oils were β-caryophyllene (0.7â5%), aromadendrene (1â6%), viridiflorene (1â7%), δ-cadinene (0.4â14%), bicyclogermacrene (0.2â10%), globulol (1â9%) and in some collections 7-epi-α-selinene (trace-9%). Key Word Index: Decaspermum humile Decaspermum struckoilicum Myrtaceaeessential oil compositionα-thujeneα-pinenebicyclogermacreneδ-cadinene