Photocatalytic disinfection of six bacteria and fungi, including pathogens of four mushroom diseases, Trichoderma harzianum, Cladobotryum varium, Spicellum roseum, and Pseudomonas tolaasii, and Escherichia coli and Bacillus subtilis, was studied. The photocatalyst reduced the number of viable microorganisms sufficiently by near-UV irradiation. Efficiency of disinfection was increased for P. tolaasii and E. coli, but not for T. harzianum, when the superhydrophilic properties of the photocatalyst were induced by 16 h irradiation of the photocatalyst by near-UV light just before treatment of microorganisms. Efficiency of disinfection was also affected by the state of the microorganisms, temperature, and the thickness of suspensions of organisms. Tests of disinfecting ability of the photocatalyst in mushroom growing rooms indicate that it can be used effectively for reducing numbers of environmental bacteria and fungi under black light, and that it was also effective under white light.