Abstract: Experimental ecology of the cercariae of Centrocestus formosanus (Nishigori, 1924) was studied from August to October 1994.It was indicated that light illumination accelerated obviously the cercariae released, cercariae showed positively phototaxis.When water temperature was 26-28℃, the time of LD50, and LD90, was about 40 and 52 hours respectively, the cercariae fully died was 56-60 hours.The relationship of dead cercariae number and time was in keeping with the logistic equation N = 820.824/1 + e6.328-0.178t Cercariae moved about in the different height water continualy but often stayed on the' bottom.Cercariae showed positively thermotaxis, the release number and sport intensity varied positively with the suitable water temperature.Cercariae could infect the fishes with auccess at the time of LD50 but couldn't at the time of LD90 Cercariae were passively carried with the water current into the mouth cavity of the host freshwater fishes and brought about the infection in the gills.