In order to better understand the occurrence of high arsenic groundwater, rare earth elements (REEs) analyses were conducted for groundwater from the Datong basin. The results indicate that high arsenic groundwater usually has low ∑REE concentration and enriches in HREEs relative to LREEs. The observed the correlation between Ce/Ce* values and Eu and Fe+Mn could be related to the reductive dissolution of Fe and Mn oxides/hydroxides. The relationship between As and Ce/Ce* value and Eu suggests that Ce/Ce* value and Eu concentration are useful indicators of arsenic mobilization in groundwater system.