The concentration of atmospheric CO2 has risen by approximately 36(null)ince the industrial revolution. However, little is known about the effects of elevated CO2 (eCO2) on the diversity, composition, structure and function of soil microbial communities. In this stud y, pyrosequencing analysis of 16S rRNA genes was used to examine the phylogenetic diversity, composition and structure of soil microbial communities and their impacts by eCO2. Pyrosequencing detected 3500 operational taxonomic units (OTUs) derived from two archaeal phyla and 18 bacterial phyla, 35 classes, 48 orders, 112 families, and 281 genera. Although the overall species richness was not significantly different between ambient CO2 (aCO2) and eCO2, both richness and evenness significantly shifted at the phylum or lower levels with species richness significantly (p < 0.10) decreased in 10 phyla (e.g., Crebarchaeota, Acidobacteria, Bacteria incertae sedis, Firmicutes, Gemmatimonadetes, Verrucomicrobia), and evenness significantly (p < 0.10) increased in Proteobacteria and decreased in Acidobacteria, Bacteria incertae sedis, Crebarchaeota, Cyanobacteria, Gemmatimonadetes, OP10, and Verrucomicrobia, suggesting the soil microbial community composition was significantly a ltered at eCO2. Especially, it appears that soil microbial populations may differentially respond to eCO2. In addition, detrended correspondence analysis (DCA) showed that the overall phylogenetic structure of soil microbial communities was altered at eCO2. Mantel tests indicated that such changes in the composition and structure of soil microbial communities were closely correlated with soil and plant properties. This study provides insights into our understanding of shifts in the composition and structure of soil microbial communities at eCO2.