The present study determined the species of cyanobacteria (CB) that are the most sensitive to the pollution of the aquatic environment with rare earth elements (REE). CB Nostoc muscorum, Nostoc paludosum, and Nostoc linckia were kept for 24 hours in model solutions with La and Ce concentrations of 0.0001 and 0.001 mg/L respectively. The titer of the cultures was from 1.2·10⁷ to 2.7·10⁷ cells/ml, the age was 5 weeks, the growth phase was exponential. Next the biochemical responses of CB were determined: the level of chlorophyll а and the concentration of malondialdehyde (MDA) in the CB homogenate. Nostoc muscorum was practically not exposed to the tested doses of REE. The effects of Nostoc linckia were maximal and most consistent. With La concentration of 0.001 mg/l the amount of chlorophyll а decreased by 4.2 times compared with the control, while intensity of lipid peroxidation (as estimated by MDA) increased by 2.2 times. These facts taken together indicate severe toxic stress. As a result the range of CB sensitivity to Ce and La pollution is as follows: Nostoc muscorum > Nostoc paludosum > Nostoc linckia. The obtained results show that even systematically and evolutionarily close biological species can differ significantly in response to toxicants.