Results of studies carried out in 1996-2000 were presented in the paper. They referred to the influence of grass communities irrigation (two mixtures with different species compositions) with purified sewage after previous mechanical and biological utilization of sewage wastes from Purification Plant Hajdów near Lublin on the yielding and species composition of grass communities. Two irrigation levels were used (600 and 1200 mm) on the background of the control object with no irrigation. In 1997-2000, irrigation was made in 10 proportional rates applying flooding system. Every year, the yield of three sward cuts was harvested and species composition was evaluated (from the 1st and 2nd cuts). Applied irrigation significantly affected the increase of mean hay yields for 4-year period in relation to not irrigated plots. Neither the varied irrigation rates nor the mixture species composition had any effects on proved yield differentiation. The irrigation stimulated the development of grasses in wet habitats (meadow foxtail, reed-grass), and reduced the share of optimum-wet-habitats species in the sward (meadow fescue, meadow-grass, meadow fescue), that dominated in the sward of not irrigated plots.