In the period 1979-1980 the phytoplankton of the Sulejow Reservoir was investigated. 543 taxa of algae were determined. In the characteristics of phytoplankton the qualitative and quantitative composition, dominant, common, and constant taxa, horizontal distribution and their seasonal changes were taken into consideration. In the upper part of the reservoir the dominants were Asterionella formosa, Cyclotella kützingiana, and Fragilaria pinnata, and in the lower one Melosira granulata, Stephanodiscus hantzschii, S. astraea var. minutulus, Fragilaria crotonensis, Aphanizomenon flos-aquae and Microcystis aeruginosa.