Objective:To analyze the results of external quality assessment (EQA) of different levels laboratories of iodine deficiency disorders (IDD) in Inner Mongolia in 2018, and to understand the detection ability of these laboratories.Methods:In 2018, the Inner Mongolia region level laboratories and all 12 league and municipal level laboratories were assessed for salt iodine, urinary iodine and water iodine (74 banner, county and district level laboratories participated in the urinary iodine assessment, and 100 banner, county and district level laboratories participated in the salt iodine assessment). As 3+-Ce 4+ catalytic spectrophotometry (WS/T 107.1-2006) was used to measure the iodine in urine, direct titrimetric method (GB/T 13025.7.1-2012) was used to measure the salt iodine, and water iodine was determined based on "Determination of Iodine in Drinking Water by As 3+-Ce 4+ Catalytic Spectrophotometry" in the range of 0 - 100 μg/L. The examination results of EQA of different levels of IDD laboratories in Inner Mongolia were statistically analyzed. Results:Regional level leboratory passed all the 3 assessments, qualified rates of salt iodine, urinary iodine and water iodine were 83.3% (10/12), 91.7% (11/12), and 100.0% (12/12), respectively, at league and municipal level; qualified rates of salt iodine and urinary iodine were 95.0% (95/100), and 90.5% (67/74), respectively, at banner, county and district level in 2018.Conclusions:The detection ability of IDD laboratories at all levels in the whole region has been stabilized, but there are still fluctuations in some laboratories. It is suggested that the technical and responsibility training, instrument verification, experimental environment control and quality control of laboratories at all levels should be continued.