Abstract. Instrumental measurements were carried out on urban tolerant Acer, Fraxinus, and Tilia species and varieties in the Buda Arboretum (N 47°28'47.7" E 19°02'19.6") in order to evaluate differences between their photosynthetic and gas exchange performance. Stomatal conductance, transpiration, net photosynthesis and photosynthetic active radiation (PAR) on sample leaves were measured and calculated using the LCi infrared gas analyzer (IRGA). Meanwhile the photosynthetic activity (net CO 2 assimilation) of leaves showed correlation to PAR, stomatal conductance and leaf temperature, there are significant differences found between genera and species of urban trees, which suggests that their CO 2 assimilation capacity differs. This influences the value of genera and species considering the urban air cleaning due to their CO 2 fixation. Under the examined conditions leaves of Tilia sp. showed higher photosynthetic capacity compared to Acer or Fraxinus sp. The transpiration rate of leaves correlates to stomatal conductance and leaf temperature. The low transpiration rate of Fraxinus excelsior 'Westhof's Glorie' leaves suggests more economic water use. We also found considerable differences in water use efficiency (WUE) between species and genera. Tilia sp. Acer platanoides and Fraxinus excelsior 'Westhof's Glorie' showed higher WUE compared to Acer negundo.