Persistent organic pollutants like dioxin, PCBs, PFOS, PFOA, and brominated flame retardants are known to disrupt thyroid hormones. Previous animal studies have reported their effects on activity and cognitive functions. Our research group utilizes IntelliCage, an automated behavior recording system, to assess exposure effects of metals such as arsenic, methylmercury, and dioxins. In this study, we investigated how hypothyroidism induces behavioral abnormalities in growth-retarded (grt) mice with congenital thyroid hypoplasia. Grt mice, characterized by a tyrosylprotein sulfotransferase 2 (Tpst2) mutation, exhibit primary hypothyroidism. Male and female grt mice were introduced into IntelliCage, and their basal activity was measured. Compared to normal mice, both male and female grt mice showed an overall trend toward decreased activity, particularly pronounced in females. Additionally, they exhibited fewer nose-pokes for water access but no significant differences in water bottle licking. These findings are consistent with reduced activity observed in congenital thyroid hypoplasia models, highlighting the reliability of IntelliCage in behavioral studies. Future research aims to utilize this system to explore cognitive function endpoints. Through our investigations, we aim to enhance understanding of the behavioral effects of chemicals inducing hypothyroidism and contribute to the development of effective evaluation methods for such effects. Further studies will expand on these findings, providing insights into the broader implications of thyroid hormone disruption on cognitive functions in animal models, and potentially informing strategies for mitigating the adverse effects of environmental pollutants on thyroid health.