Two new species of didymozoid trematodes are described from two species of Onigocia-stem platycephalid (flathead) fishes from Moreton Bay, Australia. Indodidymozoon metridion n. sp. is described fro the operculum of Suggrundus jugosus. Indodidymozoon ditremion n. sp. is described from the buccal cavity, branchial arches and pharynx of inegocia japonica. The two species can be distingished from other species in the genus Indodidymozoon, except Indodidymozoon branchiale, by their two anterior uterine loops, which are located posterior to the fore-body-hindbody junction. The new species can be differentiated from I. branchiale by the length of their testes. Indodidymozoon metridian differs from I. ditremion in body size, position of ventral sucker and relative testis length. The structure of the Laurer's canal and Juel's organ of species in the genus Indodidymozoon is discussed.