Abstract: Twenty groundwater samples and two surface water samples were collected to analyze the occurrence and distribution of iodine in groundwater in the area of Hangjinhouqi in the Hetao Plain, Inner Mongolia. The results show that concentrations of iodine in the groundwater vary between 27.30 and 1,638.00 μg/L. The concentrations of iodine in more than 50% of the groundwater samples exceed the national standard for drinking water (150 μg/L), and about 84.6% of the samples were located in high As areas. High iodine groundwater mainly occurs in the central part with slow groundwater flow and strong evaporation in the north of the study area. Furthermore, most of the high iodine groundwater is of Cl-Na, Cl·HCO3-Na and HCO3·Cl-Na types. Two mechanisms are thought to contribute to the enrichment of iodine in groundwater in this region. One is the evaporation of shallow groundwater; the other is the microorganisms in the reducing and organic matterrich deep groundwater. Comparison of these two mechanisms show that the latter is more important, however, the former is more common.