The article presents new data on vascular flora of the North-West of the European part of Russia. The data are based on our field surveys in 2021–2023, revision of herbarium collections and searching data in open sources. In the Leningrad Region, we recorded four alien species new to the Northwestern European Russia, namely Linum nervosum Waldst. et Kit., Phytolacca acinosa Roxb., Dipsacus laciniatus L., and Viscum album L., and one species new to St. Petersburg (Rhynchospora fusca (L.) W.T. Aiton), a nationally rare and protected native. The results of the study show, on the one hand, the need for further research in the region, and on the other hand, the ongoing spread of alien plant species across European Russia.