Five species of alloxystine hyperparasites of aphids are herein recognised from Australia, namely Alloxysta australiae (Ashmead), A. darci (Girault), A. fuscicornis (Hartig), A. carinata, sp. nov. and Phaenoglyphis villosa (Hartig). Hypodiranchis aphidae Froggatt is synonymised with A. fuscicornis, and Glyptoxysta bifoveata Girault with P. villosa. A key is given to the species. A. fuscicornis is the common hyperparasite of Brevicoryne brassicae (Linnaeus), the cabbage aphid; A. australiae and P. villosa are polyphagous parasites of Aphidiinae in Aphididae; and A. darci is a polyphagous parasite of Aphelinus spp. in Aphidinae. The hosts of A. carinata are unknown. Other aspects of the biology and host relations of the Alloxystinae, where known, are discussed.