© 2015, Springer Science+Business Media New York.Plants react to air pollution by increased production of reactive oxygene species and oxidative stress, which triggers multiple defense mechanisms. In this study, some parameters that serve as biomarkers for antioxidative defense, such as glutathione S-transferase (GST) activity, glutathione (GSH), malondialdehyde, chlorophyll and total soluble protein contents, were investigated on the needles of Cedrus libani (A. Rich.) grown around two industrial areas in Eskisehir. The measurements revealed that metabolism in needles of C. libani trees is largely directed towards defence against ROS, due to effects of air pollution in the sampling areas. We observed significant increases in all parameters, except chlorophyll contents, which were strongly decreased. However, these sharp changes were also prominent not only between sampling sites and control site, but also among the areas investigated, suggesting the quantitative influence of the extent of pollution. Together with total soluble protein contents, the correlation between GST activities and GSH contents suggests that damage due to oxidative stress was most probably reduced due to the increased antioxidant capacity. Therefore, we can suggest C. libani as a good model for biomonitoring atmospheric quality with the oxidative stress parameters providing an effective measure for early environmental assessment due to their sensitivities of even low levels of pollution.