Biodeterioration of library materials is a worldwide problem due to presence of huge numbers of libraries all over the world. The current research aimed to study the paper deterioration by fungi isolated from Cairo University´s old library, Egypt. The most ten frequent paper deteriorating species were used. They were Aspergillus flavus, A. niger, A. parvisclerotigenus, A. oryzae, A. tubingensis, Cladosporium cladosporioides, Penicillium commune, P. crustosum, P. digitatum and P. italicum. Artificial infestation of 4 paper types by the ten fungal species indicating variation in utilization ability depending on paper type (papyrus followed by newspaper, printer and then Whatman filter paper) and on fungal species. Determination of remaining cellulose value after paper infestation and fungal growth indicated that A. flavus was the highest cellulose utilizable in Whatman filter paper, A. niger for Papyrus paper, A. oryzae for newspaper and P. commune for printer papers. Atomic force microscope (AFM) was used in the case of P. commune infesting the 4 paper types. The images indicated a reduction in surface roughness of all paper types with Whatman paper being the most affected one. AFM indicated also disruption in the normal system of infested paper surface which appeared with many peaks compared to one peak in normal paper.