The structure and influence of selected ecological factors on ciliate communities in tree-holes of 3 tree species (Acer campestre, Carpinus betulus and Quercus dalechampii) have been analysed. In 136 samples 94 taxa of ciliates were found. Ciliates were not detected in 2 tree-holes only. An average of 3-6 species were presented in a single tree-hole, but the diversity was very irregular (0-15 species). Similarly, abundance was very irregular too and rapidly oscillated between 0-200,000 ex/ml. The frequency of individual species in the samples did not overlap the value of 30%. The highest frequency was recorded at the species Leptopharynx costalus (28.68%) and Sathrophilus mobilis (27.21%). Specifically, subclass Peritrichia was over-represented (notably species of the genera Propyxidium and Scyphidia). On the basis of Canonical Correspondence Analysis (CCA) (15 nominal and 2 gradient variables were analysed, 9 of them were statistically significant) 4 principal communities of ciliates have been distinguished. A tree species, volume and age of a tree-hole, absence of rotifers and other metazoans were revealed as critical factors with an influence on composition of the ciliate taxocoenoses. The results were evaluated by hierarchical classification (complete linkage) as well. Tree-holes of Quercus dalechampii have reached the highest species richness and were completely different from the others (Acer campestre and Carpinus betulus). Tree-holes with a volume under 1 ml and those over 500 ml had the lowest species diversity and a special position among the others. According to the age of tree-holes, the youngest and the oldest ones were linked in one cluster by Wisharts index, meanwhile the special position in the freshest tree-holes only was validated by Sørensens index. Thus the sense of time factor on a species structure of ciliate communities in tree-holes was revealed.