Objective To investigate the biodistribution of 125Ⅰ labeled dendrimer nanomaterialpolyamidoamine (PAMAM) in mice.Methods Tyrosine was conjugated to four generation PAMAM by NHydroxysuccinimide,then 125Ⅰ was labeled on PAMAM with chloramines-T method,and purified by dialysis.Labeling rate,radiochemical purity and stability of 125Ⅰ-PAMAM were detected by radioactive thin layer chromatography scanning.The gamma imaging and biodistribution were detected by in vivo imaging system and gamma counter at one,four,eight,twenty-four and forty-eight hours after intravenous injection.Results The IH nuclear magnetic resonance results showed that about two tyrosines were conjugated to PAMAM.The 125Ⅰ labeling rate was about 56％ and radiochemical purity was more than 98％.The radiochemical purity of labeled compound remained more than 90％ at 72 hours in vitro.In vivo imaging results showed that PAMAM was mainly accumulated in liver periphery.The gamma counter results showed that PAMAM mainly accumulated in liver,kidney and spleen,the excretion of PAMAM was slow and there has high dose of PAMAM in mice at 48 hours.Conclusion PAMAM with no chemical modification was mainly accumulated in liver,kidney and spleen,and the excretion of PAMAM was slow,so PAMAM is not fit as drug carrier.PAMAM need to chemical modification to accelerate excretion and prevent the emergence of toxicity caused by accumulation in body.