An annotated list of vascular plants detected in the Olonetsky State Nature Reserve (Zakaznik), located in southern Karelia, is presented for the first time. The reserve was established in 1986 in an area of 270 km2 on the basis of several protected areas of different statuses that had existed there in different time periods. Among the 444 species found, 369 (83.1 %) are native and 75 (16.9 %) are adventive. Information on exact localities, as well as on the population size and dynamics is provided for the rarest species, both native and alien. The habitats with the most distinctive flora in the reserve are xerophytic pine forests and willows thiсkets on the shore dunes and sandy beaches of Lake Ladoga, as well as swamps with black alder in the troughs between levees. Festuca sabulosa, Hypopitys monotropa, Jovibarba globifera, Oenanthe aquatica, and Viola stagnina are red-listed in Karelia. Seven more species: Scirpus radicans, Juncus balticus, Epipactis palustris, Malaxis monophyllos, Salix acutifolia, S. viminalis subsp.rossica, and S. triandra are listed in the regional Red Data Book as subject to biological surveillance. Several invasive species such as Amelanchier spicata, Aronia mitschurinii, Juncus tenuis, Lupinus polyphyllus, etc. have been found in the reserve. The expansion of the aggressive species Rosa rugosa is of particular concern. Brief information on the main kinds of human activity in the reserve which can significantly affect the composition of the flora, especially its adventive fraction, is given.