Abstract: The local biogeochemical arsenism is a kind of common endemic disease. Aiming at finding out the distribution of arsenic of different valences and its influence on disease condition, the arsenic contents in groundwater in Hetao area of Inner Mongolia are investigated. The results show positive correlation between total water arsenic content and As³⁺ content. The more the total arsenic content is, the more serious the symptoms of endemic arsenism. The longer the residents drink high-As water, the more remarkable the symptoms of arsenism are.