The article presents the results of a long-term study of the flora of the coast and islands of Lake Onega within the UNESCO World Heritage Site Petroglyphs of Lake Onega and the White Sea. A total of 395 vascular plant species are known for this area. Around the petroglyphs, the number of species varies from 39 on Cape Kladovets to 252 on the Kochkovnavolok Peninsula, the variation being mainly due to the difference in the size of the localities. The comparatively high species richness on Cape Besov Nos, on Bolshoy Golets Island, the Kochkovnavolok Peninsula and Cape Cherny is due not only to the significantly larger area, but also to a tangible human impact, leading to the emergence of alien species and active dispersal of native apophytes. Cape Cherny has the most distinctive flora, featuring 45 species (12.3 % of the total) not found in other localities. In general, the flora of the petroglyph sites is trivial and relatively unaltered by human impact; the adventitious component of the flora is small. There are few species that are red-listed or in need of monitoring on a regional scale. A finding of primary importance is Silene rupestris on Cape Cherny – the species is red-listed in the Russian Federation and the Republic of Karelia. Another regionally red-listed species encountered in the locality is Dracocephalum ruyschiana. There also occur several species subject to biological surveillance in the Republic of Karelia: Carex pseudocyperus, C. vulpina, Juncus balticus, Oenanthe aquatica, Salix acutifolia, and Thalictrum lucidum. The species checklists for 13 petroglyph locations can serve as a baseline for monitoring the flora.