Abstract: Larval African clawed frogs (Xenopus laevis) were exposed to a low dose of tributyltin (25 ng•L^-1TBTCl)for 2 months for thyroid histology observation. For one month after exposure, TBT could induce the depletion of colloid and vacuolation. And for two months after exposure, the incidence of follicle malformation also significantly increased, the relative transverse thyroid gland area and follicle area decreased sharply, and the number of follicle did not show any significant changes. Neither hypertrophy nor hyperplasia was observed between exposure groups and control ones. Therefore, the shrink of thyroid gland was arisen from the reduction of follicle area but not follicle number, and the depletion of colloid and follicle malformation was nothing with hypertrophy or hyperplasia. This study indicates that the low concentration of TBT can heavily damage thyroid histology of X. laevis, and TBT can be regarded as one of thyroid disrupting chemicals (TDCs).

Key words: thyroid disrupting chemicals (TDCs), histology, Xenopus laevis, tributyltin (TBT), thyroid disrupting chemicals (TDCs), histology, Xenopus laevis