Background. The aim of our study is to establish the current species composition of the flora of vascular plants of the National Nature Park "Zalissia" (Kyiv and Chernihiv regions, Ukraine), its analysis and identification of regional peculiarity. Methods. Research methods are classical comparative floristic, which are used for vegetation research during field trip, and its further cameral processing as well as critical analysis of the literature and herbarium data. Scientific novelty is at first on the territory of the Park, which had been closed for a long time to such research, complexes floristic inventarization studies were conducted. Results. The results of the study was analyzed and for the first time integral data on the structure of the flora were obtained. The taxonomic composition of the flora of the Park has been established (778 species and subspecies of vascular plants), which is more than half (58.5 %) of the diversity of the regional flora of Eastern Polissia. The results of the fractional and structural analysis of the flora of the Park are presented. The flora is consists of 612 native and 166 alien taxa. Systematic, life form and geographical analysis of the flora was carried out, and its peculiarities were identified. The native and alien fractions of the Park's flora were analyzed. The structural features of the native fraction of the flora reflect its rather well-defined forest character. In the family spectrum, the highest positions belong to Asteraceae, Poaceae and Rosaceae. The hemicryptophytes (65.7 %) predominate in life form spectra, and the total share of woody plants is 11.6 %. Widespread taxa are dominated, but a high share of Boreal, European, and European-sub-Mediterranean geoelements. Conclusions. The results of the fractional analysis indicate that the adventitization process dominates the synanthropization of the flora. The taxa of sub-Mediterranean origin are dominated in alien fraction flora, and American and Asian origin species have the largest number.