Abstract: In order to enrich the resources of Populus varieties in north China,female catkins were treated with 0.3%-0.5% colchicine solution during 24-96 hrs after pollination in cross combinations including(P.pseudo-simonii × P.nigra var.lica) ×(P.× beijingensis) and(P.pseudo-simonii × P.nigra var. lica) × P.pseudo-simonii,and 26 triploid plants were obtained.The results showed that 54-66 hrs after pollination was the optimal period to induce triploids in these cross combinations,and the highest ratio of obtaining triploids was 66.7%.Compared with the diploid progeny,the growth of these allo-triploids showed certain superiority.Especially in(P.pseudo-simonii × P.nigra var.lica) ×(P.× beijingensis),on average,the basal diameter and stem height of two-year-old triploid seedlings exceeded the ones of diploids by 20% and 5% respectively;the two indices of the best triploid in this cross combination were 4.42 cm and 2.77 m,which were 144% and 43% more than those of the average growth of diploids respectively.Induction of allo-triploids in Section Tacamahaca further proves that treating pollinated female catkins with colchicine is an efficient method to obtain triploid plants.