The state of microbiological air quality in indoor environments is an important factor influencing the health and well-being of occupants. In the case of library collections, it determines their durability. The aim of this study was to assess the exposure of employees and users of the university library in the building of the Faculty of Environmental Engineering of the Lublin University of Technology to bacterial and fungal aerosols. The studies were conducted during period of six months from September to February. The air samples were collected using two methods: sedimentation and impaction. Obtained results allowed for the preparation of a microbiological profile of indoor air pollution. The average concentration of bacteria in the air ranged from 0 to 990 CFU/m3 and fungi from 0 to 1736 CFU / m3, which show no air contamination. The highest concentration of bacterial microflora was recorded in October and December, and in the case of fungi, it was September and October. In the indoor air of the university library, the most common bacteria in all the examined samples were gram-positive cocci and gram-positive bacilli. In the case of fungi, Cladosporium, Penicillium and Aspergillus were the most common.