Abstract:Soil microorganisms, mainly bacteria, fungi and actinomycetes, under Eucalytus forest, Acacia forest and mixed forests were investigated during 1992 to 1993 in Huaxian county near Guangzhou. Soil enzyme activities, including cellulase, invertase, urease,proteinase and phosphate activities under different forest types were analysed. It was shown that mean annual amounts of soil dricrobes under forests are in order mixed forest>pure Acacia forest >pure Eucalyptus forest>barren and waste land. High activities of cellulase and invertase were found in "dxed forest of Acacia and Eucalyptus, while urease,proteinase and catalase in pure acacia forest. Soil respiration intensity was high in Acacia mangium forest and in its "dxed forest, and was low in Eucalyptus forest. Five years after forestation with tree species mentioned above on barren and waste land, the soil ndcroenvironment was shown to be greatly improved, which resulted in the increments of soil microbes under ground and of biomasses above ground.