Although fast-growing Populus species consume a large amount of water for biomass production, there are considerable variations in water use efficiency (WUE) across different poplar species. To compare differences in growth, WUE and anatomical properties of leaf and xylem and to examine the relationship between photosynthesis/WUE and anatomical properties of leaf and xylem, cuttings of six poplar species were grown in a botanical garden. The growth performance, photosynthesis, intrinsic WUE (WUEi), stable carbon isotope composition (δ13C) and anatomical properties of leaf and xylem were analysed in these poplar plants. Significant differences were found in growth, photosynthesis, WUEi and anatomical properties among the examined species. Populus cathayana was the clone with the fastest growth and the lowest WUEi/δ13C, whereas P. × euramericana had a considerable growth increment and the highest WUEi/δ13C. Among the analysed poplar species, the highest total stomatal density in P. cathayana was correlated with its highest stomatal conductance (gs) and lowest WUEi/δ13C. Moreover, significant correlations were observed between WUEi and abaxial stomatal density and stem vessel lumen area. These data suggest that photosynthesis, WUEi and δ13C are associated with leaf and xylem anatomy and there are tradeoffs between growth and WUEi. It is anticipated that some poplar species, e.g. P. × euramericana, are better candidates for water-limited regions and others, e.g. P. cathayana, may be better for water-abundant areas.