Abstract: The thyroid glands of eight chinese river dolphins (Lipotes vexillifer)were investigated. The thyroid of Lipotes is similar to that of the other species. The gland is a V-shaped bilobed structure. The hind ends of both lobes interconnect to a narrow isthmus. The right lobe is a little smaller than the left. In all specimens, body length is 166—244 cm, the weight of thyroid gland is 15.5—29 g. Ratio of thyroid gland weight to body weight is 0.22 g/kg. The shape of follicle is round or oval. Its average diameter is 106.4±18.7μ, and the largest one reaches 6.4 mm. The follicle epithelial cells are cubical, 6.9—14.8μ, in height and the colloid is even and eosinophil. The average diameter of parafollicular cells is 11.0μ. The histological change of thyroid in relation to different physiological condition is discussed.Three parathyroid glands were found, two situated on the ventral surface of right lobe of thyroid, another being in front of left lobe. Their shape is flat oval, and size is 0.6—1.0×0.3—0.5 cm, with 0.2 cm in thickness. The gland is divided by connective tissue septa, forming many masses and cords of epithelial cells. The mean diameter of epithelial cells is 9.7μ.