Research on the nitrogen cycle of forest soils has traditionally focused on the mechanisms regulating the turnover of inorganic N. However, the key role of organic N in soil nitrogen transformation tends to be overlooked. Over recent decades, researchers have assessed the relative importance of organic N on the nutritional requirements of plants in forest ecosystems. Most studies have revealed that soil amino acids are important sources of organic N in forest ecosystems. Although the fluxes of organic N in forest ecosystems have been studied in detail, we have a poor understanding about the role of amino acids in soil nitrogen transformation in the subtropical region of China. In this study, subtropical broad-leaved forest soil was collected from Wan Mulin Natural Reserve located at Fujian Province, southeast China. We selected four types of amino acids, including L-Glutamic acid, L-Lysine, L-Alanine, and L-Methionine as the study materials, which represented acidic, basic, neutral, and sulfur amino acids, respectively. Soils were incubated for 0, 2, 8, 12, 16, and 36 days in the laboratory after adding 0 and 40 mg N /kg amino acid. Soil moisture was maintained at 60% WHC (water-holding capacity) or 90% WHC. Ammonium N, nitrate N, soluble organic N, nitrous oxide, soil pH, and soluble organic C content were determined. Data were subjected to analysis of variance (ANOVA) with the SPSS version 18.0, and significant differences between treatments were compared by the LSD test at P < 0.05.The results showed that soil NH₄⁺-N content significantly increased with the addition of amino acids, with the repression of NH₄⁺-N production under high soil moisture content conditions (90% WHC) being relieved to some extent. Soil pH was increased by the addition of amino acids, and was closely correlated with soil NH₄⁺-N and NO₃^--N. These results support the finding that an increase in soil pH may promote N mineralization in acidic forest soils. Acidic, basic, and neutral amino acids increased NH₄⁺-N production in soil, but had little or no influence on NO₃^--N production and nitrous oxide emission. Soil nitrification was significantly inhibited by the addition of methionine, resulting in the accumulation of NH₄⁺-N. Nitrous oxide emission from soil as a whole increased with the addition of methionine. The decrease in SON under the amino acid treatments was more evident under 60% WHC than 90% WHC conditions. The turnover of amino acids in forest soil is very rapid, with NH₄⁺-N being the major N form in soil. Nitrogen transformation in forest soil is probably related to the decomposed products of amino acid mineralization, rather than the charge of amino acids. These findings indicate that nitrogen transformation varies with amino acid type, and that the mechanism inhibiting methionine during nitrification needs further research. In conclusion, amino acids might represent the intermediate products between organic nitrogen and mineral nitrogen, regulating nitrogen transformation in forest soils.