The natural flood area of PP Lonjsko polje in the lowlands of the Sava River and its tributaries has exceptional natural and cultural values. The coexistence of man and the environment in these areas had a positive and negative impact on the ecosystem. The Ramsar list has been protecting it since 1993, and 3 areas within the park are within the Natura 2000 ecological network. The results of the inventory were compared with other surveys from similar habitats. A total of 169 plant properties were determined, distributed in 50 families and 108 genera. The most represented are spermatophyta (Spermatophyta) with 164 properties, and the other 5 properties are made up of ferns (Pteridophyta). Monocots (Monocotyledonae) identified 59 properties from 11 families, and dicotyledons (Dicotyledonae) 105 properties from 34 families. All ferns are classified in the class of true ferns, except for the plant species Selaginella helvetica L., which belongs to the class of wormholes (Lycopodiopsida). Invasive and threatened intrinsic and Ellenberg indices were determined for each of its values. The average values of Ellenberg's ecological indicators for 5 habitats were analyzed. All indicators showed approximately equal average values except moisture (U). Deviations between the average moisture values (U) show the inhomogeneity of the state. According to the FCD database for Croatia, 4 invasive plant traits and 86 endangered plant traits were inventoried. Of the endangered species, especially interesting are the endangered (EN) floating species Marsillea quadrifolia L., which can only be maintained in the flora by extensive grazing and regular flooding, and the sensitive (VU) Fritillaria meleagris L., a taxon of the Croatian flora, which also needs moist and occasionally flooded meadows to survive. Invasive behavior has been replaced by the non-invasive species Glechoma hederacea L. and Potentilla reptans L. The sensitivity and biological diversity of flooded habitats require carefully designed management plans in order to preserve the ecological values of the PP Lonjsko polje area, which has been particularly threatened in recent decades due to global climate changes and large anthropogenic influence.