Abstract: Platypus cylindrus populations outbreaks observed in the last decades are related tocork oak decline in Portugal, as in other Mediterranean countries. Being an ambrosia beetle, itfeeds on fungi that carries and inoculates in galleries excavated in host trees. To study thismycobiota, fungi were isolated from the beetles (mycangia, intestine and exoskeleton) and corkoak galleries. Several fungi were identified, namely Raffaelea (Ascomycota, Ophiostomatales)and Nodulisporium (asexual stage of Biscogniauxia mediterranea), possibly implicated in hostweakness. The other isolated fungi, particularly Gliocladium, Scytalidium and Trichodermagenera, might be involved in processes such as insect feeding, wood degradation and fungalantagonism in the galleries.