The data presented here pertain to algae, specifically cyanobacteria (Cyanoprokaryota) and euglenoids (Euglenozoa), from the territory of the Slobozhanskyi National Nature Park. These data were collected during research conducted between 2013 and 2015. There is limited existing literature on algae in this area prior to the establishment of the park, and it does not include species lists. Therefore, this literature was not taken into account when creating the descriptions. One of the most notable ecosystems in the area comprises acidophilous fens found in depressions within pine forests. In historical terms, these depressions were once occupied by lakes on the river terraces. However, today, the majority of them have transformed into fens, reeds, marshes, or shallow lakes situated on the southern banks. These areas are typically characterized by the presence of Betula pubescens, Populus tremula, Alnus glutinosa, and sometimes feature Sphagnum mosses. A few depressions near Krasnokutsk still retain the characteristics of true peat bogs. They exhibit well-developed Sphagnum floating mats, open water surfaces, and a suppressed growth of pine and birch woods. These unique habitats, particularly unusual for a semi-arid region, have garnered the attention of biologists. In an effort to conserve them, the National Nature Park "Slobozhanskyi" was established in the year 2009. The primary results of the algological research have been compiled in the "Chronicles of Nature of the Slobozhanskyi National Nature Park," an annually updated report on inventory and monitoring programs. These findings have also been published in abstracts and are stored in the park's internal database. The collection of algal samples gathered within the park's territory is preserved in the algal collection of the Herbarium of V.N. Karazin Kharkiv National University (CWU). Therefore, the sources for the current dataset include the collection samples from CWU, the "Chronicles of Nature of the Slobozhanskyi National Nature Park," and the internal database.