The aim of this paper was to assess the vegetation of six lowland meadows, or study units, located in the Liw Commune. In order to meet the objectives of the research, a detailed list of species on the meadows was drawn up and a weighing analysis of vegetation in individual harvest was carried out. The research involving six meadows was carried out during the 2016 growing season. The meadows were situated in two villages: Ruchna and Ruchenka, located in the Masovian Voivodeship, Węgrów County, and the Liw Commune. The meadows under consideration occupy a total of 19 hectares. They comprise brown soil, leached and acidic, consisting of light clay, with a lower layer of heavy clay and black soil proper of very good quality, made up of light clay lying on medium clay. The soil of the meadows had a high and very high content of mineral nitrogen and magnesium, low or medium content of phosphorus, and a very low content of potassium. Three of the analyzed meadows were harvested three times, while the others were harvested four times. The results of the weighing analysis of the meadows were very varied, both between the units and between harvests. However, it should be noted that in all units the grass share, as an average of all harvest, was in majority of cases, in the range from 55% to 62%.