The changes in macrobenthos community depended on changes in stream discharge (from 0.001 m3/sec to 100 m3/sec) were studied on the basis of data from 254 stations of 180 streams located in the centre of European part of Russia. While discharge of stream increases community composition changes considerably. Species diversity increases from 12 to 47 species per station with the increase in stream size. Moreover, the diversity of almost all groups, discerned according habitat or trophic position and main taxonomic groups (with the exception of Plecoptera and Diptera) increases with the increase in stream discharge. The diversity of lithorheophilic species and species inhabiting soft substrates is higher in small streams, whereas phitophilic species are more diverse in large streams. With the increase in stream size the percent of algophagous and filter feeders increases, percent of carnivorous remains the same and the percent of detritophages decreases. The relative role of invertebrates macrotaxons change with the stream size: in the smallest streams the diversity is the highest among Diptera, Trichoptera and Plecoptera, in medium-size streams--among Trichoptera, Ephemeroptera and Diptera, in large streams--in Ephemeroptera, Gastropoda and Trichoptera. In some groups some species replace other (close-related) in parallel with change in stream discharge however in general this tendency is weak. The index of saprobic conditions increases with the increase in stream size from 1.6-1.7 to 2.3-2.4. In small streams the saprobic conditions are very different whereas large streams have tendency to be at beta-mesosaprobic level. Cluster analysis reveal four size classes of streams. Peculiarities of habitat and macrobenthos fauna of these classes are described.