Abstract: The Bayan Obo deposit, situated near Baotou, Inner Mongolia, is the largest repository of rare earth resources in the world. Bayan Obo mining district has been mined nearly 60years for iron and rare earth elements. Thorium and rare earth elements associated with minerals, were unused and heaped in two tailings which may have an adverse effect on human and animal in the environment due to their exposures. The distribution of thorium in the soil was investigated around Bayan Obo iron mining zone. Twenty-three soil samples were collected in the vicinity of Bayan Obo mining area. After digested by HNO₃, HClO_4and HF mixture in Teflon beaker, the isotope of ²³²Th in samples was determined using Inductively Coupled Plasma Mass Spectrometry. The w(²³²Th) in soil samples ranged from 3.43to 59.09mg/kg with average of 12.79mg/kg, which was apparently higher than the average values of the world (7.50mg/kg) and of China (9.88mg/kg). This indicated that the mining of the Bayan Obo, especially the two tailings may contribute to the level of thorium. The variations of ²³²Th were not obvious in vertical profiles of soil core 16and 12, further suggesting that soils near the sampling sites of 16and 12were not affected by mining activities. In comparison, the distribution of ²³²Th in the soil profile around 17sampling sites may be affected by mining activities in Bayan Obo. The contents of w(²³²Th) were low in the lower layer and high in the upper layer of the soil profile. Moreover, the w(²³²Th) steeply increased in the 10.5-17.5cm interval.