Lumbricidae play a key role in the soil environment as “the ecosystem engineers”. They participate in all the categories of services pro¬vided by ecosystems. In agricultural areas, the conventional intensive farming practices have led to a significant decline in the biological diversity of soils including earthworms. In this study, we attempted to characterize the community structure of earthworms in permanent grassland and arable land of the Didactic & Experimental Station of Rzeszów University in Krasne near Rzeszów. Similar densities of earthworms were observed in the grassland and in the arable land (101.01 ± 18.03 ind. • m-2 and 82.12 ± 18.26 ind. • m-2, respectively) (p > 0.05) as well as a similar biomass of Lumbricidae (77.72 ± 15.30 g • m-2 and 54.34 ± 11.72 g • m-2) (p > 0.05). In the research, 7 species of earthworms were found in the permanent grassland and 6 representatives of Lumbricidae were identified in the arable land. The identified earthworms represented all three main morpho-ecological groups. The density and biomass of epi-endogeic earthworm L. rubellus and the anecic species of L. terrestris were shown to be higher (p < 0.05) in the grassland as compared to the arable land. In order to protect Lumbricidae and to sustain the beneficial role of earthworms in an ecosystem, it is necessary to monitor the negative changes in populations of earthworm species attributed to various farming practices.