Abstract: A new species of trichodinids, Trichodina carassii, sp. nov. from the gills, skin and fins of Carassius auratus is described in this paper. The body diameter of this ciliate is 70(54.6—80.4) μm, the diameter of adhesive disc is 58(51.6—67.2) μm and the diameter of denticulate ring is 32(27.0—36.2) μm. The number of denticles ranges from 25 to 30. There are 7—14 granules of remains of old denticles in the centre of denticulate ring when treated with Klein's silver method. The macronucleus is horseshoe-shaped. A short rod-like micronucleus is situated outside the end of one arm of macronucleus, its position being variable. The adoral spiral of the ciliate forms a turn of about 390—400°. The blade is narrow and sickle-shaped. The thorn is relatively straight with uneven dents in the middle portion and its terminal end is round or truncated. The V-shaped corona has a small tumor at its junction with the lower arm.