Abstract: The leaves, stems and leafstalks of adult Populus tremula ×P. tremuloides were cultured to generate somaclonal lines, and the variations during culture were assayed by cytological and molecular biological methods. Only 36.81% were diploid in the 144 observed cells from regenerated lines induced by 3.0 mg.L-1 2, 4-D, which was much lower than that of the control (77.78%) and indicates that the stability of chromosome quantity of these cells was lower. The shape of chromosome of these cells also changed, with increments in length and the formation of giant chromosomes with a satellite. 54.93% were diploid in 142 observed cells from regenerated lines induced by 1.0 mg.L-1 6-BA, which indicates that the stability of chromosome quantity of these cells was between that induced by 2,4-D and that of controls. AFLP data also showed that the variation occurred at the DNA level.