An experiment has been conducted in the Experimental Station of the Nanjing Agricultural University since 1999, with the experimental fields separated into plots (2.8 m×1.0 m×0.6 m) by concrete frames.The soil in the plots was sandy loam soil (Orthic aquisols) collected from Rugao County, Jiangsu Province.The experiment was designed to be rice and wheat rotation with five treatments, i.e.application of corn residues (incorporating or mulching) with or without earthworms and control, and 3 replicates for each treatment.The responses of soil microbial biomass carbon (MBC) to earthworm act ivity had been investigated from the rice season of 2001 to the wheat season of 2004.It was found that MBC significantly increased (p<0.05) in the treatments with earthworms.Generally, the MBC was higher at the maturing stage of wheat than that in the rice season in the same year, however, the difference was notably enhanced (p< 0.05) by earthworm and weakened by input of corn straw.Posit ive effect of earthworms on MBC was more distinct in the 0~5 cm soil layer with corn residues incorporated and in the 5~10 cm soil layer with corn residues mulched.The enhancement of MBC by earthworms was similar in the 10~20 cm soil layer whether corn residue was incorporated or mulched.