The main task of protected areas is biodiversity conservation primarily concerning threatened species of plants and animals. Their value is the greater, the higher number of threatened species populations is located in this area. In Russia, conservation of species included in the Red Data Book of Russian Federation (hereafter – Russian Red Data Book plant species), has the highest priority. In this paper, we studied Russian Red Data Book plant species, known in ten protected areas of Volga Federal District (European Russia). We estimated the number of Russian Red Data Book plant species per protected area; Representativeness Index of each species per protected area; proportion of Russian Red Data Book species populations of which are being studied in protected areas; rarity categories of each plant species according to regional Red Data Books. We found out that in studied protected areas 29 Russian Red Data Book plant species are known. In different regions, populations of 6.7% to 60.0% of all Russian Red Data Book plant species are present in the studied protected areas. At the same time, Representativeness Index of these plants varied from 0.67% (Cypripedium calceolus, Bolshaya Kokshaga State Nature Reserve) to 78.6% (Thymus cimicinus, Khvalynsky National Park). Population-based studies of Russian Red Data Book plant species have not been carryed out for all of them in studied protected areas. The situation is the most favorable in Bolshaya Kokshaga State Nature Reserve and National Park ‘Smolny’, because population-based studies cover all Russian Red Data Book plant species known in these territories. In Khvalynsky National Park and Mordovia State Nature Reserve, population-based studies cover more than 50% of all Russian Red Data Book plant species known in these protected areas. There are no data on population characteristics of Russian Red Data Book plant species in National Park ‘Chavash Varmane’ (Cephalanthera rubra) and Vishersky State Nature Reserve (Calypso bulbosa, Sedum roseum). The obtained data allow us to make some recommendations concerning investigations of threatened plant species in protected areas. Firstly, we recommend to organize systematic (optimally – annual) investigations of Russian Red Data Book plant species in each protected area. Secondly, population-based studies should cover at least one population of each Russian Red Data Book plant species in protected areas. Thirdly, the obtained and analyzed data on threatened plant species should be published in journals available to wide scientific audience to avoid the loss of data.