Abstract:To explore the response of soil enzyme activities to simulated nitrogen deposition, an in situ experiment was conducted in a native evergreen broad-leaved forest in southern Sichuan. Nitrogen-addition was carried out within the forest in 2005. Four nitrogen addition treatments i.e, null nitrogen level (CK), low nitrogen level (LN， 50 kg N hm-2 a-1), moderate nitrogen level (MN,100 kg N hm-2 a-1) and high nitrogen level (HN, 150 kg N hm-2 a-1), were established in the forest. All nitrogen treatments were carried out in triplicates. All plots of treatments were laid out randomly. Beginning in July, 2005, Ammonium nitrate (NH4NO3) solution was sprayed by hand monthly onto the floor of these plots throughout the whole year. During the study period, the enzyme activities of hydrogen peroxides, urease, cellulose and invertase presented a virtical higher distribution at 0-10 cm depth than those at 10-20 cm depth. All enzyme activities changed with seasons, but their patterns varied depending on sampling time and soil layers. The peaks of activities occurred in Autumn at both soil depths of 0-10 cm and 10-20 cm for hydrogen peroxides, for urease, which occurred in Autumn at the depth of 0-10 cm and in Winter at the depth of 10-20 cm, for cellulose at both soil depths, which occurred in Spring, for invertase at the depth of 0-10 cm, which occurred in Autumn and Spring, and at the depth of 10-20 cm, which occurred only in Spring. Overall, the responses of soil enzyme activities to nitrogen deposition in the evergreen broad-leaved forests were different. Nitrogen deposition had negative effect to some degree on hydrogen peroxides activities. In contrast, the urease activities were found to be stimulated by nitrogen deposition. The results also showed that cellulose activities decreased in all treatments, whereas invertase activities increased to some degree by nitrogen deposition.