Abstract: Abstract Objective：To study the effects varying concentrations of nonylphenol on the structure and function of the thyroid gland in rats and mechanism.To provide the available information on endocrine disrupting chemical-NP to rats has on the toxic effect. Methods:40 healthy 4-weeks-old SD white rats were divided into 4 groups at random, group comprised of 5 male and 5 female rats. The treated rats were administered varying doses of NP(40mg/kg , 80mg/kg and 200mg/kg) by pouring stomach. The changes in serum hormone , histopathology and follicular cells ultramicroscopic structure were examined after 15 days. Results:1.Serum FT4 and FT3 levels decreased gradually as the dosage increased after 15 days and there is a negative correlation on doses of NP(FT4 r=-0.932; FT3 r=-0.926).The difference was statistical between random group and the treated groups(p<0.05).There was a significant difference between 40mg/kg and 80mg/kg ,200mg/kg on the doses of NP(p<0.05). 2.TSH levels increased. There is a positive correlation on doses of NP（r=0.967）.The difference was statistical between random group and the treated groups(p<0.05).There was a significant difference between 40mg/kg and 80mg/kg ,200mg/kg on the doses of NP(p<0.05). 3.SDH activity of the subject rats increased obviously , The difference was statistical between random group and the treated groups(p<0.05). 4.The hyperplastic thyroid structure can be observed on each group. The hyperplastic effect was in a dose dependent manner.

Key words: nonylphenol, thyroid gland, ultrastructure