Abstract: The water relations in saplings of Populus deltoides Bartr. cv. "lux" (ex. I-69/55), P.×euramericana (Dode) Guinier cv. I-214, P.×euramericana (Dode) Guiniercv. Sacrau-79, P.×opera Hsü and P. popularis Hsü were studied during the winter season in 1980—1982. Five poplar clones were classified into three groups according to the determinations of their monthly water contents, water saturated deficits, transpiration rates and diurnal and monthly changes of water potencials in the branches. It was find that, three clones from section Aigeiros included group Ⅰ-Populus deltoides Bartr. Cv. "lux" (ex. I-69/55) and group Ⅱ-P. ewamericana (Dode) Guinier cv. I-214 and P. euramericana (Dode) Guinier cv. Sacrau-79 have lower water content, transpiration rates and water potencials and higher water saturated deficits in branches which than other two clones from section Tacamahaca included group Ⅲ-P.×opera hsü and P.×popularis hsü. The result showes that water stress during the winter season is the main reason of lower survival rates in transplanting of poplar clones from group Ⅰ and group Ⅱ.