Foliar litter derived from trees exposed to elevated CO₂ concentration decreases in quality relative to foliar litter exposed to ambient CO₂. This change in quality could in turn affect the composition and function of microbial communities associated with litter transformation and mineralization. We evaluated the effects of decomposing litter obtained from three tree species, Pinus koraiensis, P. sylvestriformis and Quercus mongolicus, on the structure and function of microbial communities by burying litter-bags and sampling the litters at intervals over a 429-day period. Foliar litter collected from trees exposed to elevated CO₂ had greater C and lignin contents, and lost the mass at a slower rate than that collected from trees growing in ambient CO₂, except for P. koraiensis litter. The CO₂ responses of enzyme activity in litter were species-dependent. Molecular fingerprinting by means of denaturing gradient gel electrophoresis (DGGE) demonstrated that elevated CO₂ more strongly affected the fungal community than the bacterial community in decomposing litter. In samples of P. koraiensis litter that had been exposed to elevated CO₂, sequences belonging to Basidiomycota showed increases in relative intensity, which were accompanied by significant increases in enzyme activities. Our results showed that enzyme activities and micro-decomposer composition have different, litter-specific responses to changes in litter biochemistry, which indicate that exposure of trees to elevated CO₂ has varying effects on litter decomposition.