The aims of this paper were to study the biofouling and biodeterioration of books stored at the Archive of the library of Shumen University, Bulgaria, and to carry out the physiological characterization of isolated fungi and bacteria. Also the role of the environmental microbiota in the biofouling formation was studied. Microbial assemblages on documents were sampled by sedimentation method as described by Omeliansky. Biofouling were monitored by microscope and stereomicroscope OPTIKA (Italy). Large microbial assemblages were found at archive with the prevalence of genera Aspergillus, Cladosporium and Penicillium. Most of the fungi degraded cellulose and produced pigments and acids, and all of the isolated bacteria had proteolytic and/or cellulolytic activity. In shed a higher concentration of viable bacteria than of fungi was isolated. The existence of this bacterial genus in the Library of Shumen University indicates that the faulty ventilation system needs to be repaired and suitable anti-dust filters to be set.