Pentaceras australis Hook. f. is a monotypic genus of Rutaceae endemic to rainforests of northeastern New South Wales and southeastern Queensland. This study re-isolated previously reported canthin-6-one and 4-thiomethylcanthin-6-one, and first isolated and identified the 8-prenylcoumarins osthol, ramosin, and the pyranocoumarin seselin from the plant. The occurrence of 8-prenyl coumarins and their pyranocoumarin derivatives in P. australis reveals that this taxon is capable of generating at least one of the groups of secondary metabolites typical of the Rutaceae. This study also confirms that canthin-6-one derivatives are the major alkaloids in the species, which otherwise occur in the Rutaceae only in Zanthoxylum but appear to be quite widespread in the allied Simaroubaceae.