Abstract: Effect of soil fauna on decomposition of litters in Carex lasiocarpa wetland in Sanjiang Plain was studied with the litter bag technique,through analyzing decomposition rate and component contents of the litters and calorific value of the residue of decomposition.Results indicate that 1) soil fauna accelerated decomposition of the litters and the effect of macrofauna and mesofauna was more significant than that of microfauna;2) it increased concentrations of cellulose,lignin and humic acids and variation of C/N ratio of the litters,which was more significant in 16 mesh-bags than in 250 mesh-bags,suggesting that soil fauna accelerated release of components from the litters;3) the calorific value of the residue of decomposition was significantly different between 16 mesh-bags and 250 mesh-bags,suggesting that energy flow from decomposition of the litter was affected by soil fauna;and 4) soil fauna,however,did not affect much the general tendency of the decomposition,that is to say,soil fauna is not a decisive factor of the decomposition process of the litters.