Shenping village in Mouding county, Yunnan province is one of the serious Keshan disease areas, but Kaschin Beck disease has not been prevalent there yet. It is a pure Keshan disease area.Mangkeng village in Yulin county, Shaanxi province is a serious Kaschin Beck disease area to be found recently, and no Keshan disease patient has been found there. It is a pure Kaschin Beck disease area. It is very significant to compare the ecological environment in Keshan disease areas with that in Kaschin Beck disease areas for exploring the elemental difference in ecological environment between Keshan disease areas and Kaschin beck disease areas, finding out the elements related to these two endemic diseases, providing scientific basis for animal model experiment, and breaking throμgh the pathogeny of endemic diseases.The results of the research show that Se in ecological system materials such as soil, food (rice and wheat) and hair in pure Keshan disease areas in Yunnan province and pure Kaschin Beck disease areas in the north of Shaanxi province were lower than those in soil (0. 125μg/g) food (0. 025μg/g)and hair (0. 200μg/g) in non disease areas. It indicated that the ecological environment in these two endemic diseases areas were still in low Selenium status. This was the basic pathogeny of these two endemic diseases. On the other hand, the state of Se deficiency in ecological environment in pure Kaschin Beck disease area was more serious than that in pure Keshan disease areas. Comparing the chemical element in ecological system materials in both two disease areas, it was found that many elements ware significantly different. Among them, As may be a element with pathogenetic significance. As in soil. wheat and hair in pure Keshan disease area in Yunnan province were higher than those in pure Kaschin Beck disease area in the north of Shaanxi province. Because as can act against Se in biochemistry, so high As in human body may control the biological activity of Se and may reduce the pretection of Se for heart muscle, and result in the prevalence of Keshan disease. Therefore.as may be an important complex pathogenetic factor of Keshan disease.