In the course of field research, analysis of previously published works and viewing materials stored in the herbarium of the Central Siberian Botanical Garden SB RAS named after I. M. Krasnoborov (NS) we clarified an information on the distribution of rare adventive plant species in the territory of the Upper Yenisei basin. Cosmos bipinnatus, Ipomoea hederacea, Setaria maximowiczii and Sonchus oleraceus were noted for the first time in the Tuva flora, Grossularia reclinata in the Western Sayan, and Polygonum calcatum and Spergula vulgaris in the territory of Khakassia. Echinochloa crusgalli, Fagopyrum esculentum, Fragaria ananassa, Galium mollugo and Grossularia reclinata were new to the flora of the Sayano-Shushensky nature reserve. For 14 rare species new localities were noted and the boundaries of the ranges were specified: Amaranthus albus, Carduus nutans, Echinochloa crusgalli, Epilobium adenocaulon, Galium aparine, G. mollugo, Hordeum jubatum, Lactuca serriola, Oenothera biennis, Portulaca oleracea, Psammophilliella muralis, Setaria faberi, Sisymbrium loeselii, Spergula vulgaris.