State Dendrological Park "Olexandria", as the subject of natural reserve fund of Ukraine, is a structural element and a core territory of Ukraine's ecological network, which preserves the most valuable and typical for the region components of landscape and biological diversity. According to the catalogue of woody and herbaceous plants the total number of species that inhabit the territory of the Dendrological Park "Olexandria" and reflect the richness of its phytobiota has 2021 species. Sozological share of park's phytobiota are rare species that deserve high scientific attention and are officially protected because they are included to the red lists of different levels: international, national and regional, or similar legal documents for a certain category of rarity. Using the method of inventory studies the authors have found that rarity component of flora of the park includes 390 species of vascular plants, representing almost 20 % of all species of dendrological park collection. The regional steppe sozoflora includes 103 species (26 % of all rare species), the rest is 283 species that were introduced in different historical periods since the mid-nineteenth century. One hundred eighty eight (48 %) of them are woody plants, 202 species (52 %) are herbaceous plants that belongs to four divisions (Equisetophyta, Rolypodiophyta, Rynophyta, Magnoliophyta), 6 classes, 67 orders, 87 families and 199 genera. The ratio between the number of species in orders Еquisetophyta: Рolypodiophyta: Рynophуta: Magnoliophyta is 0,8 %: 1,0 %: 21,0 %: 77,2 % respectively. The ratio between Magnoliophyta and Рynophуta is 4:1. Most numerous by the number of families (59) is the class Magnoliopsida. The highest sozological capacity has Pinaceae (55 species), Сupressaceae (21), Rosaceae (29), Ranunculaceae (20), Fabaceae (19). Poaceae (16), Iridaceae (13), Lamiaceae (12), Betulaceae (11), Asteraceae (10), Cyperaceae (10) families. Also, taxonomically diverse families are Primulaceae (8), Caryophyllaceae (8), Fagaceae (7), Alliaceae (7), Corylaceae (5), Caprifoliaceae (5), Salicaceae (5), Amaryllidaceae (5), Brassiсaceae (5), Liliaceae (5). 38 (43.6 %) families of 87 are presented by one spicies. The highest species richness has: Pinus (18 species), Abies (16), Juniperus (12), Picea (12), Betula (10), Larix (7), Crataegus (7), Quercus (7), Allium (7), Carex (7), Iris (7), Stipa (6), Crocus (5) Trifolium (5) genera; 4 spicies has: Lysimachia, Chamaecyparis, Chamaecytisus, Daphnе, Malus, Prunus, Tilia. One spicies has 37 genera.