During 2009, a fungus belonging to the genus Gnomoniopsis was found associated with the necrosis of galls of Dryocosmus kuriphilus, the chestnut gall wasp. The common observation of this phenomenon in chestnut orchards prompted us to evaluate the utilization of the fungus for biological control of gall wasp. During 2011, experiments were conducted on young, five-year-old plants of Castanea sativa, situated in an orchard in central Italy. Plants were sprayed with a Gnomoniopsis sp. conidial suspension and the extent of gall necrosis, as well as the mortality of D. kuriphilus, was monitored. Preliminary results showed statistically significant differences between the galls inoculated with Gnomoniopsis sp. and the control treatment. No significant differences in incidence of fruit rot were found between treated and control branches.