Abstract: Effects of NaCl on concentrations of salt ions, glycinebetaine, reducing sugars, sucrose and soluble sugars in one-year-old seedlings of a salt-tolerant poplar genotype, Populus euphratica and one_year_old rooted cuttings of a salt-sensitive genotype, P. popularis ‘35-44’were examined. Leaf burn symptoms appeared in old leaves of P. popularis after 4 days of exposure to salinity, and young leaves in the upper shoots exhibited leaf damage and abscised by day 15. In contrast, P. euphratica had only 16% leaf loss by day 15. Leaf necrosis of P. popularis was the result of excessive salt accumulation, and P. euphratica exhibited a greater ability to exclude Na+ and to limit Cl-transport from roots to leaves under increasing salinity. In addition, genotypic variation of salt resistance was related to the accumulation of compatible solutes. Leaf betaine content of P. euphratica increased 244_fold on day 15, up to 1899.8 μmol/L, and a 10-fold rise was also observed in roots. Similarly, levels of reducing sugars, sucrose and total soluble sugars significantly rised and reached the maximum on day 4 (leaf) and day 15 (root), respectively. By contrast, betaine levels of P. popularis declined following salt stress and no significant rise of sugars was observed in leaves and roots during the period of salt stress. Therefore, we concluded that the accumulation of compatible solutes made contributions to salt resistance of P. euphratica.