Because of the fast growth and organ development, infant is believed to be one of the most vulnerable cohorts to the risks of environmental pollutants. Calculated by body weight, infants may burden more pollutants than adults. It is because they have immature metabolic system, and they are exposed to more chemicals like phthalates through several different routes including digestion, inhalation and skin contact than adults. The developmental stage-specific physiological behaviors, metabolic mechanisms and capacities add more uncertainty to the infant exposure risk and health risk than to the adult. Our previous study indicated that infant may expose more some phthalates such as DBP than adult. Due to the potential health risk of phthalates, the proposal intends to investigate infants' developmental stage-specific exposure to these pollutants and the metabolic capacity in pollutant clearance. By using follow-up biomonitoring, we will investigate infants' phthalate body burden and their metabolite profiles at each of the developmental stages, including 0-1, 1-3, 3-6, 6-12 month old and 1-2 year old. Referencing to phthalates' metabolic capacity and its dynamic changes in liver microsomes from baby rats, infants' developmental stage-specific metabolism of phthalates will be characterized by combining with the biomonitoring data and exposure factor questionnaires. Finally the study would contribute to some basic knowledge of infant exposure risk to phthalates, and in further, could refine the infant cohort risk assessment.