Plant residue can be an important factor regulating the emission of greenhouse gases, such as nitrous oxide (N₂O). We conducted an 84-d laboratory incubation to examine the effects of plant residues on soil N₂O emission, microbial respiration and net N mineralization under aerobic (i.e., 30% and 60% water filled pore space (WFPS)) and oxygen-limited (i.e., 90% WFPS and fluctuation between 30% and 90% WFPS) conditions. Plant residues with C:N ratios ranging from 14 to 297 were added into a Wickham sandy loam soil collected from an organic farm at 4 mg C g^-1 soil. Plant residue addition enhanced soil N₂O emission by up to ~ 82% and 136% at 30% and 60% WFPS, respectively, but reduced soil N₂O emission by up to ~ 90% and 95% at 90% WFPS and the fluctuation, respectively. These plant residue-associated effects appeared to be related to their C:N ratios. Enhancing effects at aerobic conditions were inversely related to the C:N ratios of plant residues; by contrast, the reducing effects at oxygen-limited conditions were positively related to the C:N ratios of plant residues. While plant residue addition has been considered to stimulate denitrification, thereby the production of nitrogen gases under oxygen-limited conditions, our results demonstrated that N₂O emission was greatly reduced by plant residue addition.