A checklist of the vascular plants occurring in the Narew National Park (NE Poland) is presented, together with a 5-degree evaluation of species occurrence frequency. Field surveys carried out in 2000–2001 have yielded records of 659 species, belonging to 89 families. Most abundantly represented families are: Asteraceae (with 72 species), Poaceae (68), Rosaceae (40), Cyperaceae (36), Fabaceae (36), Caryophyllaceae (31) and Lamiaceae (30). Among the growth-forms, perennials are most abundant, accounting for 66% of all species. Annuals (terophytes) comprise 21%, whereas trees and shrubs make up 13% of the flora. The flora of Narew National Park is dominated by species characteristic of reedbeds (Phragmition) and tall sedge beds (Magnocaricion), and those occurring in swamp woodlands and shrubs (Alnetea glutinosae). The largest species-richness is found in swamp woodlands, meadows and, most of all, in dry grasslands and oak-hornbeam forests on mineral islands. Such rare and endangered (in north-east Poland) species like Dianthus superbus, Gentiana pneumonanthe, Iris sibirica, Potentilla rupestris and Salix starkeana are recorded on the habitats of the last type. The alien species that have been noted in the national park, including particularly invasive ones, as: Acer negundo, Echinocystis lobata,