Epiphytic lichen diversity were investigated on 11 Quercus taxa in Marmara Region and effect of bark pH was evaluated on the lichen diversity. Overall 88 lichen taxa were recorded. Q. petraea was determined the richest oak with 47 lichen taxa while Q. hartwissiana was determined the most poor oak with 7 lichen taxa. The highest average bark pH (6,16) was recorded from Q. frainetto and the lowest average bark pH (4,76) was recorded from Q. cerris. Since bark pH values of the investigated Quercus taxa are usually high, nitrophytic species were more observed than acidophytic species on barks. In this study, we observed that bark pH values were varied among Quercus taxa and localities. Heavy fertilization practises in Marmara Region were observed effect of bark pH of Quercus taxa in the several localities which near the agricultural areas