Abstract: Prey composition of the Japanese treefrog, Hyla japonica GÜNTHER, 1859, was investigated in an area invaded by the Argentine ant, Linepithema humile (Mayr, 1868). Ants were the most common taxa among the prey animals in young treefrogs, constituting 82.4% of the numeric proportion and 49.9% of the volumetric proportion of all prey items in the frog stomachs. Among ants, Argentine ants were most abundant; 333 workers (52.2% of all ants) were found in 36 frogs (85.7% of frogs examined), indicating that Argentine ants are palatable to the treefrogs.