Compared with terrestial and marine ecosystems, freshwater ecosystems, including rivers and lakes, are relatively closed, with low feed-back capacity and stability. However, freshwaterness is one of the major resources that human beings live on. In the past decades, due to erosion caused by deforestation, reduction in lake area caused by drainage to creat arable land, damage to fish resources caused by over exploitation and interception of lakes from rivers, pollution caused by discharge of industrial waste water, and eutrophication caused by discharge of urban sewage, the natural freshwater biodiversity has been damaged to various extents, and reduction in biodiversity has cuased damage to the structure and fuctioning of the freshwater ecosystems, decreasing the availability of this renewable resource. This paper discusses some aspects of biological diversity in Chinese freshwater ecosystems that are of prime importance for research.