The Ova of Fasciola hepatica, Fasciolopsis buski and Clonorchis sinensis were observed under the scanning electron microscope. An apparent operculum is found in the egg of each shecies studied. The diameter of the operculum is 23.5-34.6 um for F. hepatica, 16.1-21.0 um for F. buski and 4.94-5.93um for C. sinensis respectively. All opercula in the egg of C. sinensis were tightly closed, while some opercula in the eggs of the other two species studied were either detached from the egg or partly opened. Eggs of both F. hepatica and F. buski are relatiuely smooth. in C. sinensis, the egg possesses interweaving microfilamentous processes, with 0.87-2.16um wide.