Objective To understand the trend of iodine nutritional status of 8-10 year-old children and pregnant women in Lai’an County after the concentration of iodized salt in Anhui Province was adjusted from 35 mg/kg to 25 mg/kg in 2012. Methods Yangying Township of Lai'an County was selected as the observation point.A new standard iodized salt was supplied in 2012,i.e.salt iodine concentration of 25mg/kg.The iodine nutritional status of children and pregnant women was tested at 1, 2, 3, 6, 9 and 12 months after implementation.From 2014 to 2016, a follow-up survey was carried out annually in this town.The survey was recorded as the first and second in time sequence.The second, third, fourth, fifth, sixth, seventh, eighth and ninth surveys were conducted.200 children aged 8-10 years old in a primary school in this town were monitored.Urine samples and salt in children's homes were collected for detection of urinary iodine and iodized salt content, and 50 pregnant women were sampled in this township for investigation of urinary iodine and salt iodine content. Results In the baseline survey of children and these 9 monitoring assessments, the median values of salt iodine in the home of children aged 8 to 10 years were 29.2, 23.2, 22.1, 23.8, 23.2, 23.6, 22.4, 22.5, 23.0 and 22.2 mg/kg, respectively. There were significant differences in salt iodine content between children aged 8 to 10 years and between the baseline and each evaluation (P＜ 0.001, after correction test level a = 0.0028). The median urinary iodine levels of children aged 8-10 years in baseline survey and the first to ninth evaluation were 335.2, 279.2, 306.6, 337.3, 260.8, 274.9, 196.0, 220.4, 241.1 and 159.4 μg/L, respectively. There were significant differences in urinary iodine concentrations of children aged 8-10 years between baseline and 4th to 9th assessments.(P＜0.001, after correction test level a=0.0028). The median values of salt iodine in the home of pregnant women were 27.3, 24.5, 19.9, 22.7, 24.0, 22.2, 21.2, 19.9, 20.3 and 22.1 mg/kg in the baseline survey and the first-to-ninth evaluation, respectively. The difference of salt iodine content in the home of pregnant women was statistically significant between the baseline survey and each evaluation (P＜ 0.001, adjusted test level a= 0.0028).The median urinary iodine of pregnant women in baseline survey and the first to ninth evaluation were 300.7, - (missing)、 193.4, 192.4, 249.6, 198.1, 173.3, 240.3, 207.2 and 174.2 ug/L, respectively.Compared with baseline results, there was no significant difference in urinary iodine concentration between pregnant women in the 4th, 5th, 7th and 8th evaluation and baseline pregnant women (adjusted test level a=0.0031). Conclusion After the implementation of the new iodized salt standard,the iodine nutrition level of children aged 8-10 gradually decreased to the appropriate level and the iodine nutrition level of pregnant women decreased gradually from greater than the appropriate amount to the lower limit of the suitable level.According to this result, pregnant women were more sensitive than children to the lowering of salt iodization standards, and they have a risk of insufficient iodine nutrition.