Objective:To explore whether polychlorinated biphenyl 118 (PCB118)could cause inflammation reaction in rat thyroid. Methods:①Forty male Wistar rats were randomly divided into 4 groups:solvent control group (corn oil),low dose,medium dose and high dose PCB118 groups,intraperitoneal injected with corn oil or different doses of PCB118 (10,100,1 000 μg/(kg-d),respectively)for 5 d per week,and weekly weighed. Thirteen weeks later,the thyroid tissues were stained using HE method and the infiltration of inflammatory cells were observed. ② The effects of PCB118 on FRTL-5 cells viability was assessed using a Cell Counting Kit-8 assay. ③Quantitative real-time PCR (qRT-PCR)was used to detect the mRNA expression of cytokines interleukin-6 (IL-6),tumor necrosis factor-α (TNF-α) and intercellular adhesion molecule-1 (ICAM-1 ). Results: ①In HE staining,there were a large number of inflammatory cells infiltration in PCB118-treated rat thyroid tissue; ②Relatively low concentrations of PCB118 had no significant effects on cells viability(P > 0.05); ③Compared to the control group,the mRNA levels of IL-6,TNF-α and ICAM-1 increased significantly(P < 0.05) after stimulating with different concentrations of PCB118. Conclusion:PCB118 could induce inflammation reaction in rat thyroid tissues.