The results of the analysis of the diversity of rare algae of Ukraine are presented. The discussion is the basis for inclusion in the fourth edition of the Red Data Book of Ukraine the species Aegagropila linnaei Kütz. (Cladophorales, Chlorophyta), Paludicola keratophyta (Bory) M.L.Vis et Necchi (Batrachospermales, Rhodophyta) and Lychnothamnus barbatus (Meyen) Leonhardi (Charales, Charophyta). Their descriptions, nomenclature history, ecological features and typological timing are given. Summarized information on the distribution of known species proposed for protection at the state level in Ukraine and the world. The publication is illustrated with original photos and drawings. The information is supplemented by maps with the indicated localities of growth.