We conducted researches on fruiting phenology and small mammals’ activity in well- and less-drained peat swamp forests to test the effect of drainage on fruiting phenology of tree species. To test the activity of small mammals, we conducted seed removal experiment. The removal rate of model seeds decreased during flooding season, whilst it increased during lower watertable, indicating that flooding restricted feeding activity of terrestrial small mammals which are the dominant seed predators. Species well preferred by seed predators produced seeds during flooding season, while less preferred species produce seeds ignorant to flooding condition. The result indicate well preferred species fruit flooding season to avoid seed predation. Compared with well- and less- drained forests, most of the study species were fruited more frequently in well-drained forest than in less-drained forest. This indicates drainage does not negatively affect fruiting. Possible explanations for the observed phenomena are that drained condition is less stressful for plant species as their root can directly respirate, and drainage enhances mineralization of nutrients as tropical peat decompose and release nutrients under aerobic condition.