By using follow-up biomonitoring, the dynamic change of infant urinary 17a-ethynylestradiol and hormone related to hypothalamic pituitary gonadal axis at each of the developmental stages (from birth to 6 months), was investigated. Combining with infant health physical examination and questionnaire data, we will demonstrate infants’ ethinylestradiol exposure level and body burden, illustrate the changing mode of sex hormone during the period of mini puberty, and further study the possible endocrine disturbing effect.