Growth pattern, intra and inter annual variability of δ13C in the poplar clones (Populus x euramericana hybrids) at two different sites were investigated. High growth variation was found among the clones present at Migron as no definite growth pattern was followed by the clones. BAI for the clones went on increasing till the rotation time. At Begaar the trees followed the same pattern of growth, in which there was a first slow growth period, then a rapid growth period, which then stabilizes and finally a mature growth period. However, there were some marker years found in which the growth was suppressed due to drought like 1998, 2003 and 2005. Intra annual variations for δ13C was dominated by δ13C depleted early wood and δ13C enriched latewood at both sites with little clonal variations. Fritzi Pauley at Migron and I 214 at Begaar were found to be more water use efficient than others. There was a significant clonal difference found at both sites for WUE. A moderate positive relationship was found between the BAIre1 and δ13C at Begaar, in which the δ13Cwas positively correlated with BAIre1. I 45/51 was the most productive clone with highest tree diameter at the rotation time and was found to be highly water use efficient after Fritzi Pauley.