Abstract <p>Data on the fauna of soil nematodes and the structure of their communities under the invasion of Sosnowsky’s hogweed <i>Heracleum sosnowskyi</i> Manden. into northern meadow ecosystems have been first obtained. The study was conducted in the Republic of Karelia in the locations where some of the most extensive densities of hogweed growth currently exist (Essoila village, Pryazhinsky district; Shuya village, Prionezhsky district). The study showed that the abundance and taxonomic diversity of soil nematodes in the hogweed habitats varied greatly. Bacterial feeders and omnivorous and plant-associated nematodes dominated in the community structure, meaning that trophic groups of nematodes with a wide range of nutrition were highly abundant. On the basis of a comparative analysis of data obtained from two model sites—a monodominant plant community formed by hogweed and a meadow biocenosis—the changes in main characteristics of nematode communities occurring upon hogweed introduction into meadow ecosystems were identified. It was found that, under hogweed invasion, dominant nematode genera and the ratio of trophic groups changed. However, the total number of identified nematode taxa remained almost the same. Thus, the introduction of a new alien plant species into natural communities does not lead to a significant decrease in the nematode fauna diversity. Regression analysis revealed statistically significant patterns between a number of parameters characterizing soil nematode communities (total nematode abundance, Margalef’s richness index, relative abundances of some trophic groups) and the following environmental factors: soil acidity and total carbon and nitrogen content. Thus, the results obtained also allowed assessment of the role of soil conditions as factors in the formation of soil nematode communities under <i>H. sosnowskyi</i> invasion into meadow ecosystems.</p>