The epiphytic diversity of lichens associated with Quercus cerris L. and Quercus frainetto Ten. were investigated in 21 localities of the Marmara region. A total of 106 taxa belonging to 49 genera were reported on Q. cerris and Q. frainetto, and 16 of those taxa were recorded for the first time in the Marmara region. The number of lichen species found on Q. cerris was 83, while 85 taxa were found on Q. frainetto. Several differences regarding the lichen taxa were found in these 2 oaks species even though they were growing in the same habitat and in the same locality. Furthermore, some morphological, anatomical, and ecological peculiarities, as well as the phytogeographical patterns of the recorded lichen taxa, were evaluated. The majority of the lichen species were hygrophytic and mesophytic. In addition, nitrophytic species were more frequently observed than acidophytes. Temperate and suboceanic species were the most common.