Abstract: 3 cultivars of Populus deltoides Marsh and 4 cultivars of P. x euramericana (Dode) Guinier are used as male and/or female parents to carry out 7 species and/or cultivars combinations of hybridizatios in this test. The F1 hybrids of these combinations have been studied for 8 years (1982~1990) and 3 combinations among them have been selected as good combinations which are Populus deltoides cv. 'LUX' × p. deltoides cv. 'Shan Hai Guan', P. deltoides cv. 'Shan Hai Guan' × P. deltoides cv.'Harvard' and P. x euramericana cv. 'San Martino'× P. deltoides cv.'Shan Hai Guan'. At age 4, the hybrids of these 3 combinations exceeded P. x euramericana cv. Sacran 79 (control) in height by 23%~37.5% and in breast high diameter by 26.5%~81.5% and expressed obvious hybrid vigor. The F1 hybrids of P. deltoides cv. × p. deltoides cv. differentiate a fewer morphological forms and their growth rate is higher than that of their parents and control. From these hybrids we have obtained some new clones which possess such characteristics as high quality and fast growth. The F1 hybrids of P. x euramericana cv. × P. x euramericana cv. differentiate more morphological forms which grow relatively slowly. The transgressive inheritance in growth rate of these hybrids is less or negative and it is impossible to choose any clone surppassing control in growth rate from them. The F1 hybrids of P. deltoides cv. × P. x euramericana cv. are the intermediate forms of the above mentioned F, hybrids. Since the growth rate of these hybrids is relatively high, it is possible to choose some ideal clones from them.