Abstract: Based on the successful polyploidy breeding experience of other plants, this paper tried to find some means and ways, by using the male flower buds of Ginkgo biloba growing in Beijing,to induce doubling pollen chromosome with various concentrations of colchicines in different treatments. With 0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 0.6% colchicines, doubling pollen chromosome on both flower branches cultured in water and trees growing naturally were tried respectively and the differences of inducing effects under two conditions were analyzed. The results indicated that the large size pollen was obtained from the buds treated by colchicine in the soaked cotton on trees, but the obtaining percentages were relatively low with the highest one 7%. It is estimated that there will be a corresponding increase of large size pollen by increasing the concentration of colchicine and prolonging treatment time. Whereas, the large size pollen was not found by treating flower branch cultured in water, the reasons and optimal ways were still being probed. The DNA relative content of large unreduced pollen grains induced by colchicine was determined quantitatively with laser scanning confocal microscopy (LSCM) using the normal-sized pollen grains as control. The results suggest that the large unreduced pollen grains are diploid.