Rainforest in the tropical savanna landscapes of monsoonal Australia is of high biogeographic interest because it occurs as numerous small and isolated patches, and supports a fauna that contrasts markedly with that of the surrounding savanna. The overall ant fauna of monsoonal rainforest is known reasonably well, but with just one exception (Holmes Jungle in Darwin) the faunas of individual rainforest patches have been only superficially studied. This paper comprehensively documents an ant fauna of a spring-fed rainforest patch at the Territory Wildlife Park (TWP) near Darwin, contrasts it with that of surrounding savanna, and compares it with the Holmes Jungle fauna. Ants were sampled at 21 locations within the TWP rainforest, using Winkler sacs for litter-dwelling species (160 samples), standard pitfall traps for ground-active species (75 traps), and baited pitfall traps taped to trees for arboreal species (75 traps). In total, 43 species were collected, with 35 recorded in leaf litter, 24 in ground pitfall traps and 12 in arboreal pitfall traps. Species of Paratrechina and Pheidole collectively comprised 75% of all individuals recorded. Species richness was far higher in the surrounding savanna, and the rainforest and savanna faunas had markedly different species and functional group composition. The rainforest fauna at TWP was remarkably similar to that at Holmes Jungle. The rainforest/savanna contrast in ant diversity across northern Australia is the reverse of that occurring in Neotropical savanna landscapes.