A multiple-regression model is presented for estimating the effect of major air pollutants on net photosynthetic rate (Pn) of Quercus mongolica leaves, of which visible injury is not shown. Photosynthetic capacity was found to be primarily a function of PPFD, air temperature (T) and ambient ozone (O3) concentraton. The negative direction of photosynthetic capacity response to O3 concentration indicates a potential growth reduction of Q. mongolica due to ambient O3 concentration in the urban areas of Korea. The model was compared with a non-linear regression model including the same variables. We assessed the contributin of variables to two models of ambient O3 affecting Pn of Q. mongolica leaves. The mean Pn difference between the models with and without ambient O3 in the multiple-regression was smaller than that in the non-linear regression. The relative contributions of ambient O3 to multiple-regressio and non-linear regression were 12.6% and 5.6%, respectively. The results indicate that multiple-regression models can be applicable for qualitative or quantitative assessment of the effect fo air pollutants on Pn response of plant leaves, of which visible injury may not be shown in situ. Also, the assessment of ecophysiological effects using numerical models will have a degree of uncertainty associated with the measuring time/period fo the field data used in the modelling as well as the numerical structure of the models.