To assess the relationships between blood lead levels and thyroid functional tests in battery industry workers. This cross-sectional study was performed on 100 personnel of a battery factory in 2019. The checklist including demographic information of employees (age, sex, work experience, smoking, etc.) of the work shift, work environment, and duration of work was completed. Venous blood samples were also taken from the participants to check blood levels of lead and thyroid hormones. The mean age of participants was 36.1 ± 5.6 years and their mean TSH and lead levels were 3.69 ± 2.45 mIU/L and 297.9 ± 174.2 μg/L, respectively. Participants were divided into two groups based on job duties: administrative and working in the production line. Participants were divided into two groups based on blood lead levels: normal (less than 300 μg/L) and high lead level (more than 300 μg/L). Only the work experience between these two groups was significantly different and was higher in the high lead group compared to the normal lead group and no significant difference was observed between different groups based on lead level in terms of TSH level and thyroid hormones. Our study showed that although the amount of whole blood lead concentration is not related to thyroid hormone levels and thyroid function, but with increasing work experience, the amount of whole blood lead also increases significantly and since lead poisoning can have many health hazards, employers must plan to minimize the lead exposure of workers and provide protective equipment for workers.