Abstract: We investigated the effects of Populus euphratica apyrase genes (PeAPY1 and PeAPY2) on salt tolerance of higher plants. Using PeAPY1 and PeAPY2 transgenic plants, Atapy1 and Atapy2 mutants, Arabidopsis wild type (WT) and vector controls (VC), we examined the effects of NaCl on root length, relative electrolyte leakage, cell viability, H₂O₂, extracellular ATP (eATP) and antioxidant enzyme activities. Results showed that the low salinity (50 mmol/L NaCl) had no significant effects on root growth, physiological and biochemical parameters. However, a high salinity (100 mmol/L NaCl) markedly reduced root length, cell viability and activities of antioxidant enzymes (superoxide dismutase /SOD, ascorbate peroxidase /APX, catalase /CAT). In contrast, the high NaCl increased relative electrolyte leakage, H₂O₂, and eATP levels in all the tested lines. PeAPY1/2-transgenic lines exhibited a less pronounced effects as compared with the Arabidopsis Atapy mutants under high salinity. We inferred that the overexpression of PeAPY1/2 led to an up-regulated apyrase, which hydrolyzed eATP and down-regulated the ATP induction of H₂O₂. Moreover, PeAPY1/2 -transgenic lines maintained activity of antioxidant enzymes under salt stress. This would reduce the membrane peroxidation induced by the reactive oxygen species. As a result, the membrane integrity and cell viability were less affected by salt stress, leading to an increased salt tolerance in PeAPY1/2-transgenic plants.