Fast-growing tree species are widely used as pioneers for reforestation. These plantations strongly affect the ecosystem productivity and nutrient cycling, whereas their effect on the soil microbial community is still unclear. In a reforestation chronosequence in subtropical China consisting of Eucalyptus plantation with ages of 1, 2, 4 or 5 years, we examined the response of the soil microbial community and its function. The results showed that soil bulk density and dissolved organic carbon decreased significantly along the chronosequence. Soil pH was highest in the 5-year-old plantation. The amount of bacterial phospholipid fatty acids (PLFAs) and arbuscular mycorrhizal fungal PLFAs increased, but the ratio of fungal-to-bacterial PLFAs decreased with increasing forest age. The composition of the soil microbial community obviously changed after 5 years' development. Redundancy analysis showed that dissolved organic carbon was the major factor associated with the changes of soil microbial community composition. The short-rotation Eucalyptus plantation could affect the composition of soil microbial communities through changing soil available carbon when planted in subtropical region at the early developmental stage. We suggest that soil microbial community composition should be taken into consideration in the large-scale reforestation activities. Copyright © 2012 John Wiley & Sons, Ltd.