According to the results of the study of the flora of the natural monument of regional natural monument «Pe-trovskoe swamp» (Russia, Bryansk Region, Mglinsky district), carried out in 2018–2019, annotated lists of vas-cular plants and bryophytes were compiled. The flora of vascular plants includes 367 species from 80 families. The largest number of species is found in the families Asteraceae (40 species), Poaceae (34), Rosaceae (25), Fabaceae (19), Cyperaceae, Lamiaceae and Apiaceae (17), Caryophyllaceae (13), Ranunculaceae (15), Brassi-caceae and Scrophylariaceae (10). 5 of these species are listed in the regional Red Data Book (Krasnaia..., 2016): Diphasiastrum complanatum, Juniperus communis, Lathyrus pisiformis, Pulsatilla patens, Sanicula europaea. Alien species were recorded, including those spreading from cultivated coenoses in nearby settlements: Acer negundo, Amelanchier spicata, Echinocystis lobata, Helianthus tuberosus, Hemerocallis fulva, Hesperis pycnotricha, Levisticum officinalis, Oxalis stricta, Rudbeckia laciniata, Saponaria officinali, Sorbaria sorbifolia. Bryophytes belong to 107 species in 41 families. New localities of mosses listed in the regional Red Data Book were discovered: Homalia trichomanoides, Neckera pennata, Sphagnum jensenii. Indicator species of old-growth forests were noted: Anomodon longifolius, Homalia trichomanoides, Hypnum cupressiforme, Neckera pennata, Stereodon pallescens.