Abstract: The objective of this study was to investigate the influence of Lmethionine on nitrification and nitrous oxide emission in a red soil under laboratory incubation experiments. A subtropical broadleaved forest soil sample was collected from Wanmulin natural reserve in Fujian Province, Southeast China. Five treatments were carried out with three replications, i.e., control (CK), Lmethionine addition (M), Lmethionine and NH₄⁺-N addition (MA), Lmethionine and NO₂^--N addition (MN), Lmethionine and glucose addition (MC). The soil moisture was maintained at 60% WHC or 90% WHC. The results indicated that the soil NH₄⁺-N content in the M treatment significantly increased by 0.8%-61.3%, while the soil NO₃^--N content reduced by 13.2%-40.7% compared with CK. Under 60% WHC condition, soil NO₂^--N content in the MC treatment was higher than in the M treatment, soil NO₃^--N content in the MA and MN treatments were greater than that in the M treatment, and greater in the MN treatment than in the MA treatment. The soil NO₃^--N content was lowest in the M treatment after incubation. These results suggested that Lmethionine could inhibit nitrosation process of autotrophic nitrification. To some extent, carbon addition as glucose with Lmethionine decreased the NH₄⁺-N content, inhibited the autotrophic nitrification and their effects were dependent on water level. Under 90% WHC condition, carbon addition improved denitrification more obviously, but the decrease of NO₃^--N content was not sufficient to prove the inhibition of heteronitrification due to carbon addition in the presence of Lmethionine. The nitrous oxide emission from soil was increased by Lmethionine addition. Compared with 60% WHC condition, the nitrous oxide emission was higher under 90% WHC condition, and the pr