Objective To evaluate the stability of urinary iodine concentration(UIC) of school-age children and examine its representativeness for iodine nutritional status of their parents in order to provide a scientific basis for monitoring and control of iodine deficiency disorders.Methods A cluster sampling method was used,respectively,to recruit 748 and 640 children aged 8-10 in primary schools of Harbin city and surrounding rural areas.A random urine sample was collected once a day for three consecutive days in September 2011.Meanwhile,a parallel questionnaire survey was conducted about iodine-rich food (northern most common foods including kelp,seaweed and other seafood) intake status,during the urine sample collecting period and three days prior to the urine sample collection.UIC of those children,who consumed no iodine-rich food during the urine sample collecting period and three days prior to the urine sample collect ion,was measured by arsenic cerium catalytic spectrophotometry and analyzed in order to evaluate the stability of UIC of school-age children in three consecutive days under relatively constant dietary iodine intake.In addition,a household survey was carried out in rural areas; a random urine sample of 37 children's parents (25 fathers and 33 mothers) was collected once a day to measure UIC for exploring the representativeness of UIC of children for iodine nutritional status of their parents under daily similar diet.Average daily salt intake of 30 urban and 37 rural children was investigated by "three days weighing method",and 37 salt samples were collected from 37 families of children in rural areas to measure iodine concentration with the same method.Results There were 440 and 342 children who did not consume iodine-rich food in the urban and the rural survey sites,respectively.Under relatively constant dietary iodine intake,the medians urinary iodine of UIC of urban children in three consecutive days were 198,188 and 187 μg/L,and there was no statistically significant difference between groups (x2 =1.7,P ＞ 0.05) ; the medians urinary iodineof UIC of rural children were 257,232 and 202 μg/L,and there was a statistically significant difference between groups (x2 =39.3,P ＜ 0.01) ; after pairwise comparisons,the differences were statistically significant (all P ＜ 0.01).Furthermore,the ratios of urban and rural schoolchildren with UIC measurement ＜ 100 μg/L in three consecutive days were 12.7％(7/55) and 0(0/24),respectively; while ＞ 300 μg/L were 11.0％(8/73) and 22.2％(28/126),respectively.Moreover,Pearson test showed that the correlation between UIC of children and their parents was very low (r =0.10 and 0.25,respectively).Besides,average daily salt intake of urban and rural children were (6.4 ± 2.0)g and (6.6 ± 3.4)g.Average iodine concentration in household salt samples was (25.7 ± 10.8)mg/kg.Conclusions UIC in school-age children under relatively constant dietary iodine intake is fluctuating.Besides,a random UIC of children is not a good representative of their parents.When assessing the iodine nutritional status,repeated investigation should be conducted in order to make results more reliable and comprehensive.