Abstract: Triploid induction in white poplar(Populous alla×P.glandulosa and P.tomentosa) by the chromosome doubling of megasppore was studied.The results were as the followings:a cytological study of megaspore mother cells(MMCs) and pollen mother cells(PMCs) meiosis revealed that there was a close association between MMCs and PMCs meiotic stage of P.alba × P.glandulosa during the development under the same environmental conditions.Based on the association,the meiotic stages of MMCs were determined timely by the PMCs meiosis and treated effectively to induce 2n female gametes.While the pollen developed into mid-uninucleate microspore stage,a high doubling efficiency of triploids reaching 16.7% was obtained in the late leptotene stage of megaspore,which was the optimal treatment stage for chromosoeme doubling of megaspore in P.alla×P.glandulosa.Two-year-old triploid (P.alla×P.glandulosa) × P.tomentosa is characterized by the properties of fast growth,large and vigor.