Objective To study whether the measure of consumption of iodized salt to prevent iodine deficiency disorders could lead to residents excessive iodine intake in the coastal areas in China.Methods A large population-based cross-sectional study was carried out in four typical costal provinces along the coastline from north to south,including Liaoning,Shanghai,Zhejiang and Fujian.In addition to survey all of its area of Shanghai,the other three provinces' investigation was carried out at urban and rural levels,respectively,including 5 costal cities,5 costal villages and 3 inland rural areas(as a control point) in each province.In each investigated spot,the local water iodine,residents qualified iodized salt consumption rate,per capita daily intake of salt and urinary iodine levels in different populations were investigated.Results A total of 7552 copies of drinking water samples,7996 salt samples and 9873 urine samples of different populations(adults,lactating women,pregnant women and children) were collected from the 4 provinces.Except the coastal cities and counties of Zhejiang province,the qualified iodized salt consumption rates at household were all greater than 90％ in the investigated spots.The median urinary iodine(MUI) of adults and children investigated in the costal areas were in the range of 100 - 299μg/L.The MUIs of lactating women of all investigated areas were all greater than 100 μg/L.The MUI of pregnant women was at an insufficient iodine level which was lower than 150 μg/L in Shanghai,the costal cities of Zhejiang and the coastal counties of Fujian.Conclusions The overall level of iodine nutrition of coastal residents is appropriate; and it is insufficient among pregnant women in some coastal areas; coastal areas should adhere to the salt iodization measures to control iodine deficiency disorders.