Upper Ordovician radiolarians are described from limestone within the Malongulli Formation in the Cliefden Caves area using revised systematics. Eight genera and 12 species are described, including the following four new species: Protoceratoikiscum crossingi, Haplotaeniatum ovatum, Haplotaeniatum prolatum, and Borisella dunhilli, and two new combinations, Borisella subulata and Haplotaeniatum spongium. All samples are dominated by Kalimnasphaera maculosa, B. subulata, and Palaeoephippium octaramosum with lesser abundances of Haplotaeniaum spp. and Inanigutta complanata, and rare occurrences of Protoceratoikicsum spp. The rare species Etymalbaillella yennienii is reported for the first time outside of China. The Malongulli Formation is upper Eastonian through lower Bolindian (Katian global stage) based on graptolite and conodont biostratigraphy. From a stratigraphic standpoint, the limestone intervals sampled appear to represent two or possibly three stratigraphically separate intervals within the Malongulli Formation. Conodonts recovered from Coppermine Creek, Angullong/Belubula, and Gleesons Creek localities occur in the lower and middle parts of the formation and fall within one conodont zone, the O. velicuspis Zone. The stratigraphic position of the limestone at the Sugarloaf Creek locality is higher, possibly as high as lower Bolindian, based on proximity to the top of the formation where Bolindian graptolites have been recovered. Despite the different stratigraphic positions of the limestones, the radiolarians contained within are essentially the same fauna, barring some differences in relative abundance in Haplotaeniatum and Palaeoephippium. The Malongulli fauna is discussed with respect to other Upper Ordovician faunas, most notably those from siliceous facies in the eastern Lachlan Orogen and from the Hanson Creek Formation of Nevada, U.S. The radiolarian species occur across different depositional environments and from a range of geographically widespread localities, which bodes well for them being recognized as biostratigraphically important faunal markers with correlation potential within the Katian.