Ecological and coenotic properties are given and the environmental importance of natural complexes of the Emerald Network of Ukraine «Mozh river valley» (UA0000299 Mozh river valley) in Kharkiv region is highlighted. The object is located in the valley of the Mozh River — a right-bank tributary of the Siverskyi Donets River (Don River Basin) and covers 12658.48 hectares; moreover this area has hardly undergone changes due to land reclamation measures. In addition, the emerald object includes the reserves of local significance «Mirgorodsky» and «Merefyansky», as well as the wetland «Zaplava r. Mzha». The investigated object currently represents a complex of various identified settlements from Resolution 4 of the Berne Convention (C1.222, C1.224, C1.225, C1.32, C1.33, C2.33, C2.34, D5.2, D6.1, E2.2, E3.4, E5.4, F9.1, F3.247, F3.4, G1.11, G1.36, G1.414, G1.51, G3.4232, G1.A1), which have natural-historical and geomorphological dependance. The main ecological and biotic features, areas and list of main plant species are given for them. In the studied area there are populations of rare species of vascular plants that have different sozological status. Annex I to Resolution 6 of the Bern Convention includes Jurinea cyanoides and Pulsatilla patens, and a number of species have state preservation status in Ukraine (Salvinia natans, Dactylorhisa incarnatа, D. fuchsia, D. majalis, Orchis palustris, Gladiolus tenius, Fritillaria ruthenica, Tulipa quercetorum, Stipa borysthenica, Pulsatilla pratensis) and at the regional level (Polygonum bistorta, Valeriana officinalis, Parnassia palustris, Veratrum lobelianum, Thelypteris palustris, Dryopteris cristata, D. carthusiana, Athyrium filix-femina, Chrysosplenium alternifolium, Comarum palustre, Carex pseudocyperus, Lycopodium clavatum, Orthila secunda, Rubus saxatilis, Dianthus stenocalyx). In case of increasing economic impact, the main conditions for the existence of natural complexes in this area is the necessity to streamline forest use, reduce the impact of a number of invasive tree and shrub species, and minimize the impact of drainage and plowing of floodplains. It is also necessary to regulate the stream of vacationers and reduce the degree of anthropogenic pressure on natural complexes.