Persistency of grass associations is one of the way to counteract degradation of grasslands. The objective of the investigations carried out in 9-11 years of pasture use was to evaluate Poa pratensis persistence in sward. In the years 2005-07 Poa pratensis made 22.3-47.6% in the first regrowth of grass-clover sward and 39.3-52.1% of grass sward. The last two years were marked by a clear decrease of the studied species amount in the pasture association, irrespective of sward type and N fertilization dose. However, it was noted that the further increase of Poa trivialis and Deschampsia caespitosa share in spring sward, while Trifolium repens and Dactylis glomerata in summer. The higher competitiveness of Dactylis glomerata under conditions less suitable for Kentucky bluegrass development induced pasture productivity stabilization. Yet a higher abundance of this species in summer, like the growing Poa trivialis contribution in spring sward regrowth, has not ensured stabilization of pasture association in a marshy habitat.