Our dataset includes 7950 records of small mammals (Erinaceomorpha, Soricomorpha, Chiroptera and Rodentia) in Mordovia State Nature Reserve and National Park “Smolny” (European Russia). The data on 35 species of micromammals belonging to 4 orders, 21 genera and 9 families are presented. The dataset summarizes small mammals’ occurrences obtained by field studies in the territory of this protected area between 2018 to 2023. Each occurrence record contains the species name, basis of record, age and sex of studied animals, females’ reproductive conditions, geographic coordinates, coordinate accuracy, date of the record and authors of the record and species identification. All occurrence records are georeferenced. The dataset is based on research of the staff of the Institute of Ecology of the Volga River basin of the Russian Academy of Sciences and the Joint Directorate of the Mordovia State Nature Reserve and National Park “Smolny”. A major part of the data set was obtained during our helminthological study of micromammals. Another part of the data was obtained when studying ecology and abundance of chiropterans using mist nets. Our studies of rodents and insectivores were conducted by trap lines and direct observations in nature.