Soil ciliates are an important component of microfauna and play a crucial role in the functioning of microbial food webs by mediating the flux of both substances and energy in many soil ecosystems. As they response to the changes of environmental conditions more quickly than other organisms, they have increasingly been used as a robust bio-indicator in bioassessment of soil environments. In order to obtain a better understanding on the toxicity of ent-kaurane diterpenoids to the soil ciliates, the effects of this toxin on the community structure, abundance and feeding habit of soil ciliates were detected. The bioassay of ent-kaurane diterpenoids on soil ciliate communities was conducted using a pot simulation test in the Mayan Forest Region of the National Nature Reserve of Xiaolongshan. The ent-kaurane diterpenoids were mixed with the soil at arrange of concentrations: 0, 2.5, 12.5, 22.5, 32.5, 42.5, 52.5, 62.5, 72.5 and 82.5 mg/kg dry soil. Three replicates were carried out for each treatment. The pots were treated in a greenhouse for 60 days, during which the ciliate community structures were evaluated using the non-flooded Petri dish method and the abundance of ciliates were estimated using direct counting method. Ciliate species were identified using living observation and silver impregnation. The residue concentrations of ent-kaurane diterpenoids and the abundance of ciliates were measured at the time interval of 1, 3, 8, 15, 30 and 60 days. A total of 88 species were identified, belonging to 42 genera, 29 families, 11 orders and 3 classes, of which 75 taxa were found in the samples of control. Analyzes using two-factor ANOVA showed that the effects of ent-kaurane diterpenoids on the numbers of ciliate species represented significant differences among the treatments with a arrange of toxin concentrations (F_5,9=137.776,P＜0.01) and that the samples within different exposure time (F_5,9 =2.607,P＜0.05). The regression analyses demonstrated that species number of ciliates decreased with increasing concentrations of diterpenoids. This finding suggested that the toxin diterpenoids may resulted in a degraded succession in community structure of soil ciliates. Both dominant species and C/P quotient were changed at the concentrations of ent-kaurane diterpenoids more than 32.5mg/kg, i.e., the ciliate communities were dominated by Colpoda inflata, Cyrtolophosis elongata, Leptopharynx eurystoma and Cyclidium oblongum, followed by Colpoda inflata, Cyrtolophosis elongata, Cyclidium muscicola, Leptopharynx sphagnetorum and Halteria grandinella, and the C/P quotient were changed into the values more than one that indicates the community structures were strongly disturbed. However, Halteria grandinella, Oxytricha minor, Leptopharynx costatus and Frontonia sp. dominated the communities at the concentrations of ent-kaurane diterpenoids more than 62.5mg/kg. The analyses of the ciliate feeding habits suggest that the diterpenoids represented a significant inhibition on carnivores. Furthermore, it was also shown that Colpodida presented high tolerance to ent-kaurane diterpenoids, compared to Hypotrichida, Prostomatida and Nassulida. Otherwise, the abundances of soil ciliates definitely decreased at different concentrations of diterpenoids within the same exposure time compared with the control, while the cell number of ciliates represented an increased trend with extending exposure time at same toxin concentration. The growth of ciliates can be inhibited even at considerably low residual concentrations of diterpenoids. K-independent sample of nonparametric tests indicated that there were significant differences in the abundance of ciliates among the treatments at different toxin concentrations. These findings suggest that the community structures of soil ciliates were strongly disturbed at different concentrations of diterpenoids in terms of both species composition and abundance.