Aims: To evaluate whether decoloured cell-free supernatant of Lysobacter enzymogenes C3 can decrease paper bioreceptivity to fungal attack. Methods and Results: To prepare colourless C3 supernatant, single-factor design and uniform design were applied. The optimum conditions with high decolouration degree and low antifungal activity loss were achieved as follows: carbon granule content 1.6% (M/V), temperature 27 degrees C, decolouring time 1.2 h and pH 8.0. An agar plate bioassay was used to assess the antifungal activity of the decoloured supernatant against the fungal isolates obtained from contaminated books, and strong suppression was observed. Small-sacle laboratory test was further introduced, in which common book papers were artificially inoculated with the fungal isolates, and then sprayed uniformly with decoloured supernatant or water. The results showed that, after treatment, the paper showed a significantly low extent of fungal colonization and high tensile strength, and maintained the same colour before and after treatment. Conclusion: These results suggest that the decoloured C3 supernatant inhibits fungal growth on types of paper commonly used in books. Significance and Impact of the Study: Decoloured C3 supernatant could be used as a preventive agent to protect books and other paper-based items against fungal growth.