An ecological study of the testate amoebae fauna in Durankulak Lake (Northeastern Bulgaria) revealed 91 taxa, belonging to 20 genera. The genera Difflugia (34 species), Centropyxis (14), Arcella (6) and Difflugiella (6) had the highest species diversity. The species Trinema enchelys (31.2% relative abundance), Euglypha rotunda (15.1%) and Microchlamys patella (6.6%) were present with high population density and were dominants in the lake. The species richness and abundance of testaceans differed considerably among separate localities. By the mean of some basic indices for structure of communities, a characterization of the diversity of testate amoebae was made.