The study was conducted in the old, historical park, in the northern part of Stalowa Wola city (south-eastern Poland). The aim of the study was to investigate the diversity of moss-inhabiting diatoms of the white poplar (Populus alba L.) bark. During the study, a total of 47 diatom taxa were found, of which three were considered as dominat. Three other species are mentioned in the Red List of the Algae in Poland: Achnanthes coarctata (Brébisson) Grunow, Luticola acidoclinata Lange-Bertalot and Stauroneis thermicola (Petersen) Lund. For three species: Luticola sparsipunctata Levkov, Metzeltin & Pavlov, L. vanheurckii Van de Vijver & Levkov and Hantzschia subrupestris Lange-Bertalot is the first report from Poland.