Three p-HOC6H4COOR (R = Me, Et, Pr) parabens were studied for ecotoxicity on bacteria Vibrio fischeri, single-celled algae Pseudokirchneriella subcapitata and Desmodesmus subspicatus, higher plants Lemna minor and crustaceans Daphnia magna. Biocidic activity of the parabens increased with increasing the R chain length. The studied parabens did not create any significant danger for aquatic organisms.