Objective To study the effect of iodine deficiency or excess on physical development of the second filial generation(F2) of Balb/c mice.Methods The mice were randomly divided into five groups(LI,NI,5 HI,10 HI,50 HI) by fed with water of different level of iodine.After three months,the mice mated and their second filial generations of 20-day and 40-day were observed.Results The serum thyroxine levels were lower than the normal in LI and 50 HI groups of 20-day and 40-day F2 mice.Compared with the second filial generation of 20-day mice in NI group,the weight of the body was decreased in LI group;the weight of the body,spleen,thymus were decreased,the length of the body,tail were shortened and the relative weight of the brain was increased in 50HI group.Compared with the second filial generation of 40-day mice in NI group,the weight of the body,spleen,thymus,adrenal gland were decreased,the length of the body was shorten and the relative weight of the brain was increased in LI group;the weight of the body was decreased and the length of the body,tail were shortened in 50HI group.Conclusions In mice,iodine deficiency and excess can cause hypothyroidism,then affect the physical development,and condition is more serious in iodine deficiency group.Balb/c mouse have high endurance to iodine excess,the development is later in 50HI group.