There is a rising concern about the ecological safety and potential health risks caused by pesticides that are commonly present in the environment. Previous studies have shown that metabolites of pesticides sometimes possess more potent endocrine activity than the parent compounds. However very little efforts had been devoted to evaluate the environmental risks of pesticide metabolites. In the present study, we evaluated the agonistic and antagonistic activities of fipronil and its metabolite, fipronil sulfone, and compared by in vitro reporter gene assays using CHO-K1 cells. For estrogenic and antiestrogenic activities, both fipronil and fipronil sulfone showed no agonistic activities but exhibited the similarly antagonistic activities via estrogen receptor α (ERα), with the RIC20 of 6.4 × 10(-7)M and 9.8 × 10(-7)M, respectively. In the thyroid hormone receptor (TR) assay, only fipronil sulfone showed anti-thyroid hormone activity with the RIC20 of 8.2 × 10(-7)M. Furthermore, molecular docking was employed to support the results in TR assay with lower MolDock score for fipronil sulfone. Data provided here suggested that it is of great significance to study the endocrine-disrupting effects of pesticide's metabolites, especially those with persistence in environment and high toxicity to non-targeted organisms.