Invasive plant species are naturalized, foreigns, intentionally or unintentionally introduced to the territory of the Republic of Croatia. According to the World Association for the Conservation of Nature, invasive species represent the second major cause of threat to native species. With the Flora Croatica Database tool, about 617 allochthonous species have been registered in Croatia, of which 70 are invasive. The problem of invasive species was caused by man himself, creating new types of habitats such as arable land, parks, gardens, etc., thus providing suitable conditions for their development. East part of Slavonski Brod, along the Sava River, is 1500 ha of floodplain of which about 280 ha is Gajna, typical Slavonian pasture enriched by wetland flora and fauna. By a request submitted by the Brod Ecological Society (BED) and on the proposal of the Republic Institute for Nature Conservation, on September 14, 1990, Gajna was granted the status of a significant landscape by a decision of the Municipal Assembly of Slavonski Brod. The vision of BED is preserving landscapes that are disappearing, protection of nature and biodiversity, preserving indigenous breeds, traditional construction methods, etc. The aim of the final paper is to determine which invasive plant species are found in the floodplain of Gajna, to describe their morphology, ways of distribution and possibilities of suppression. During the 2019 growing season, the following invasive species were identified in the Gajna floodplain: Ambrosia artemisiifolia L., Amorpha fruticosa L., Asclepias syriaca L., Conyza cadanensis L. Cronquist, Erigeron annus L. Pers., Veronica persica Poir. and Xanthium strumarium L. ssp. italicum (Moretti) D. Löve.