Books and documents are subject to decay by a variety of organisms, including mould. Experiments were conducted to find the lowest gamma radiation dose needed to inactivate fungi. Aspergillus versicolor and Eurotium chevalieri, previously isolated from naturally contaminated book from a Brazilian public library and from the environment, respectively, were cultivated and treated in a Co60 irradiation unit with doses ranging from 14.5 to 25 kGy. The minimum dose required to kill these fungi was 16 kGy. Thus, this dose was applied directly to a severely attacked book and deteriorated old documents. Pieces of damaged paper from these materials were incubated in culture media before and after the treatment. Several fungi were isolated and identified, including representatives of Acremonium, Aspergillus, Cladosporium, Fusarium, Penicillium and Trichosporon. After the treatment, no living fungi were detected from the irradiated material. The book was maintained in favorable conditions for new fungal attack for 2 months and no fungal growth was detected. These results are very promising and demonstrate the effectiveness of gamma-ray radiation for the recovery of severely damaged books and old documents, leading to the preservation of our cultural heritage and prevention of diseases caused by moulds in libraries and archives.