Increasing need for energy with economic growth and industrialization has led to increased air pollution. In addition to the health impact on residents of the city, air pollution also affects the trees. One of the most important trees which is widely planted in Isfahan is sycamore ( Platanus orientalis L. ). In the present study, various air pollution stress indicators on sycamore were measured. It was done in different bases including cell biochemistry, leaf morphology and crown condition. Then their relation to different pollutant concentrations such as ozone, nitrous oxide, nitrogen dioxide, sulfur dioxide, carbon dioxide and particulates was investigated. There is four permanent air quality monitoring stations in Isfahan . To achieve the goal, three sycamore similar trees with almost the same conditions near the stations were selected for leaf sampling and crown imaging. In addition, AOT 40 index for protecting forests was calculated. The mean concentration of aformentioned pollutant was 37.77, 72.24, 36.21, 21.68, 6.20 and 168.07 ?g/m 3 , respectively. The total sulfur concentration in the leaves showed a negative correlation with NO 2 . There was not any significant correlation between total sulfur concentration in leaves and SO 2 . Tow-way ANOVA results showed significant changes in total sulfur concentration in leaves during different times and SO 2 levels. In all seasons except fall, the total sulfur concentration in sycamore leaves was higher in SO 2 polluted area. Sulfate ion concentration in leaves increased from spring to fall. In other words, the inorganic sulfur was accumulated in the leaves of sycamore. In spring, sulfate ion concentration showed a negative correlation with nitrous oxide (NO). Pigments and their ratios showed little correlation with the concentrations of air pollutants, but generally carotenoids responded better to air pollution than chlorophylls. Chlorophyll a and chlorophyll b showed negative correlation with NO in autumn. In spring, total leaf carotenoids showed negative significant correlation with ozone and it showed positive significant correlation with NO. It was also negatively correlated with NO. Chlorophyll a to chlorophyll b ratio showed negative significant correlation with NO in spring and the entire year. Specific leaf area showed a strong relation with ozone, nitrogen dioxide, nitrous oxide, and carbon monoxide so it was a good indicator of air pollution stress and damage to sycamore. The average leaf size showed positive significant correlation with NO2 in spring. It also showed positive correlation with NO in summer and showed positive correlation with AOT40 and NO in whole year but it showed negative correlation with CO in spring. Air pollutants affected the average leaf size by inducing premature leaf scenesense and consequently new leaf flush. Branch density varied at different stations. During a long time, air pollution has changed crown form to a dense and small canopy. The leaf to branch ratio showed positive significant correlation with NO 2 and negative significant correlation with CO in all seasons. Yellowing of sycamore leaves in Isfahan starts in early summer. Average crown color showed negative significant correlation with NO and PM 10 (p 0.01) and positive significant correlation with O 3 (p .05) in fall. AOT 40 index showed better relation with plant parameters than ozone. So our results confirm the use of this index to show the ozone damage to plants. Key words : Air pollution, sycamore, leaf biochemistry, leaf morphology, crown condition, crown color, Isfahan