Summary Species composition, abundance and diversity estimates are given for testate amoebae from seven different Sphagnum peatlands in southwestern Ontario, Canada. A total of 35 taxa or species groups in 18 genera are recorded. Assulina muscorum was found to occur in every sample. Cyclopyxis arcelloides-type, Hyalosphenia subflava and Sphenoderia lenta characterize moderately dry sites (78–89 % peat water content), and Hyalosphenia elegans, H. papilio, Phryganella acropodia, Heleopera sphagni and Nebela collaris characterize moderately wet sites (90 to 95 % peat water content). Densities were greatest in dry sites. Diversity increases with increasing moisture and community evenness is greatest in moderately dry sites. The Sphagnum peatlands in southern Ontario typically contain faunas that are adapted to minerotrophy, seasonal and periodic drying and moisture fluctuations, and a humid, continental climate.