Abstract: The function of several slime-for ming bacteria on the formation of soil water-stable aggregates was studied. The results show that the bacteria significantly promote the formation of soil water-stable aggregates (＞0.25mm). The secondary metabolites rather than the cells play a more important role in promoting soil aggregate formation. The stimulating effect changes with the supply of diff erent organic materials.Sucrose as a sole carbon resource of the bacteria, much better than either wheat or corn straw, gives a highest soil water-stable aggregates (＞0.25mm). Loenardite does not have a significant promoting effect on the aggregate formation. There are obvious differences in promoting aggregate formation by the bacteria with adding different carbon resources.