Selenium is one of essential trace elements for human and animal.In order to study some endemic diseases in relation to environmental selenium,the distribution of Se in soils of Shaanzi Province was investigated.The quaternary loess and granite with low-Se content are predominant in parent materials of the soils in Shaangi.The average total Se content of soils developed on these parent materials is 0.118 ppm,and the average content of water-soluble Se is 1.9 ppb.Most of them belong to the.soils defecient in Se.Seleniferous rocks and soils are only distributed in limited areas of the eaatern Bashan Mountains of Southern Shaangi.According to the geographical distribution of Se in soils of Shaangi Province,five regions are divided as follows:(1) the region of very low content of Se,including Maowusu desert region and Loess Plateau in Northern Shaangi;(2) the region of lower content of Se,including Guanzhong Plain and "Sanbian" closed flow depression;(3) the region of medium content of Se,including Hanzhong-Ankang Basin;(4) the region of variable content of Se,including Qinling and Bashan Mountains;(5) the region of medium-high content of Se,including the eastern Bashan Mountain.The Se content of topsoil is the highest,and it decreases with the increasing of depth gradually in soil profile.There is a better correlation of exponential function between the percentage of water-soluble Se and soil pH,the regression equation is y=0.027e^0.53x,r=0.763.The content of soil water-soluble Se is dependent on the total Se content,organic matter content and pH of soil.The regression equation of three variables is as follows:y=-7.148+0.014x₁+0.128x₂+0.93x₃,r=0.785.Among the three factors mentioned above,the total Se and pH are the primary and the organic matter is the secondary.