The species of genus Paulownia ( Paulowniaceae) have high rate of CO2 assimilation and efficient use of photosynthetic photon fluxes(PPFD), allowing them to achieve high growth rates. We investigated the response of gas exchange, in the first year of vegetative development of two clones of Paulownia elongata x fortunei established at three sites conditions different edaphoclimatic(Trehualemu, El Vergel and La Isla) located in the regions of Maule and Biobio, in central Chile. Gas exchange was measured monthly six leaves(of different plants) per clone per site using PPFD of 1500 mu mol +/- photons/m(2)/s, determining net photosynthesis (An), transpiration (E), stomatal conductance (Gs) and instantaneous water use efficiency (WUE) calculated as the An/E ratio. The net photosynthetic response (A) to PPFD of 2400, 1500, 1200, 900, 750, 400, 150, 100 and 0 mu mol photons/m(2)/s was measured monthly in a leaf of a plant per clone per site using equipment IRGA.With the set of data pairs (A, PPFD) obtained for each site, clone and month, adjusted light curves. To determine significant differences between clones, the parameters obtained from the adjusted were compared. As a result it was determined that depending on the site and clone, the last month of measurement, high net photosynthetic response (A) between 19.7 and 33.4 mu mol CO2/m(2)/s were achieved to the 2400 mu mol photons/m(2)/s, not being light saturation (A(sat)), obtaining at the same time compensation points between 96 and 69 mu mol photons/m(2)/s (when A= 0), respectively, indicating that the high intensity of radiation is an important environmental factor in the regulation of photosynthesis of the studied clones. The variance analysis of gas exchange showed presence of interaction site x clone in An, Gs and E, not in WUE; reaching in places with higher content of water (CH) maximum values of An between 17.1 and 21.3 mu mol CO2/m(2)/s with difference not significant between clones, in comparison to the site with smaller CH which presents values of An between 12.4 and 19.2 mu mol CO2/m(2)/s, differing significantly between clone. The changes of An are significantly affected by Gs and E. The parameters of the model adjusted with data of A/PPFD, did not show significant differences between clones in sites with best edaphoclimatic conditions, in particular, higher content of water available in the soil for plants. It is determined that for crops of these clones in Chile is necessary selecting sites that have edaphoclimatic conditions similar at site El Vergel.