New control strategies are necessary for the treatment of the bacterial diseases of hazelnut (Corylus avellana) incited by Pseudomonas avellanae and Xanthomonas arboricola pv. corylina, following the programmed phasing out of copper-based anti-cryptogamics. Based on recent evidence gathered on many crops, endophytic fungi are credited for playing a role as defensive mutualists of plants. Thus, an investigation was carried out in the hazelnut growing areas in Southern Italy in the aim to identify endophytic fungi possessing antimicrobial properties against these two pathogens. A panel of 50 endophytic isolates was selected, including species which are already known as being part of the hazelnut mycobiome, along with a few new records. These isolates were tested for antibiosis in an in vitro assay consisting in the inoculation of the two bacterial pathogens in their culture filtrates. Four isolates, belonging to Cladosporium perangustum, Talaromyces purpureogenus, Nemania diffusa and the Hypoxylon fuscum species complex, displayed consistent inhibitory effects, inducing about 90% growth suppression of both bacteria. Their capacity to effectively act as biocontrol agents will be further tested in planta