Abstract: In this paper, it is first reported that a new disease caused by one kind of endoparasitic ciliate has existed among the cage-cultured large yellow croakers in Luoyuan Bay, Fuzhou, China. The temperature to the occurrence of the ciliate disease is 17 ℃ ~ 22 ℃, and its daily mortality has reached 1~2%. Microscopic examination showed that this kind of ciliate parasitized in the body surface mucus, fin, gill, liver, spleen, kidney, intestine, and brain tissue. Among which, the great marjority of the ciliate existed in the branchial vessels. The author has put up one dose of Chinese herbal formula, compounded of eleven kinds of traditional Chinese medicines, such as Stemona sessilifolia, Cortex Phellodendri Chinensis，Sophora flavescens，Fructus Cnidii，Poria cocos. After having given the treatment orally for 15 days, it has achieved a remarkable result. This case has strongly indicated that the Chinese herbal formula can be used for large yellow croaker in the prevention and treatment of endoparasitic ciliate disease.