【Objective】Eucalyptus is one of the main tree species introduced into the country for afforestation because of its fast growth and economic value. By the end of 2015, its plantation had expanded up to 4 500 000 hm2. Afforestation of fast-growing Eucalyptus has received considerable attention with regard to its impacts on forest ecosystem. It is now known to affect physical and chemical properties of the soil, and plant community biodiversity. A number of studies have shown that it causes the soil degrading once it takes the place of native forests, but still little has been reported on its effects on soil microbial communities in South China. Soil microbial communities play a central role in litter decomposition, nutrient mineralization, and nearly all soil ecological processes in forest ecosystems, and may serve as an early indicator of changes in soil because of its rapid response to anthropogenic disturbances relative to soil biogeochemical properties. Litter decomposition provides the main source for soil microbial communities in forest ecosystems, whereas decomposition of Eucalyptus litter can disrupt the ecological associations between soil microbial communities and previous native communities. It is, therefore, very important to understand impacts of decomposition of Eucalyptus litter on structure and functions of the soil microbial community and its mechanisms to elucidating impacts of a single plant species on ecosystem services. 【Method】 A simulation pot experiment was laid out in random block design and designed to determine impacts of Eucalyptus litter on structure and functions of the soil microbial community by means of comparison with mixed litter of natural secondary forest. Three types of natural secondary forest soils different in soil carbon and nitrogen contents were used in the experiment. A portion, 2 g each, of air-dried litter was mixed separately with 200 g (dry weight) soil in each pot, except for control (no litter added). Structure and functions of the soil microbial community in the soil of each pot were determined with the PLFA (phospholipid fatty acids) and BIOLOG (single carbon metabolism) methods, 10, 20 and 30 days after the decomposition started. 【Result】 Results show: (1) Eucalyptus litter was higher in carbon content but lower in nitrogen content than the litter of natural secondary forest, and so significantly higher in carbon-nitrogen ratio; (2) PLFA abundances of bacteria, fungi, actinomyces and total PLFA were significantly higher in the soil treated with Eucalyptus litter than in the soil of the control, but significantly lower than in the soils treated with natural secondary forest litter; Principal component analysis (PCA) of the PLFA data shows that the treatment of Eucalyptus litter differed significantly from the treatments of mixed natural secondary forest litter in soil microbial community structure, and principal component one (PC1) explained 84.02% of the variation; and (3) PCA of the BIOLOG data also shows that significant differences existed between treatments in carbon utilization profiles of the soil microbial community, and PC1 and PC2 explained 36.99% and 16.95% of the variation, respectively; the treatment of Eucalyptus litter significantly lower than the treatments of natural secondary forest litter in carbon metabolic intensity, richness and diversity of soil microbial community, too. 【Conclusion】 All the findings in this study demonstrate that Eucalyptus litter is lower in capability of supplying soil microbial communities with adequate habitat and food than the mixed natural secondary forest litter.