Abstract: The oak pinhole borer, Platypus cylindrus, is one of the few ‘ambrosia beetles’ found in Mediterranean basin countries. Attacks of this insect are related to cork oak decline in the majority of stands, particularly in Portugal, while in Tunisia the insect is less widespread. Ambrosia beetles bore into xylem of their host trees and construct galleries to lay eggs and breed in the wood. The larvae feed on specific fungi, known as ‘‘ambrosia fungi’’ that are transported by the adult insects to newly colonized trees, and cultivated on the wall of the galleries. The objective of this work is to compare the mycobiota associated with P. cylindrus in Portugal and Tunisia aiming to discuss its role in tree decline considering the different cork oak forest management in both countries, with different intensity levels of exploitation. Logs of infested cork oak trees were collected from seven stands located in the Western North of Tunisia (Ain Beya, Ain Sarouia, Babouch, Belif, Hamdia, Mzara and Oued Zen) during 2011. In Portugal, the samples were taken in 2007 from four stands in the two main cork producing provinces, Alentejo and Ribatejo. Insects were retrieved from infested logs and fungi isolation was made both from the insects and their galleries. A considerable fungal diversity was found in the material studied, reflected in the values of the Shannon-Weaver ecological diversity index. Fungi belonging to the genera Acremonium, Biscogniauxia, Botryosphaeria, Fusarium, Gliocladium, Ophiostoma sensu lato (Ophiostomatales), Scytalidium and Trichoderma were isolated from the material of Portugal and Tunisia but in different proportions. Ophiostomatales were found as the main symbiotic fungi of P. cylindrus in both countries, confirming the stability of this association and its possible role in cork oak colonization and decline.