Abstract: The effects of colchicine treatments on relative-germination rate and potential of seeds for four Betula platyphylla families were studied. The treatment combinations included the colchicine concentration of 0.1% and 0.2% and the treatment time of 1 day, 2, 3 and 4 days. Based on the results of first experiment, the second one was further to investigate the inducing rate of tetraploid after applying the treatment combination of 0..2% and 3 days on 7 families of two species, B. platyphylla 伊B. pendula and B. pendula. Results of the first experiment showed that the colchicine concentration had a significant influence on seed relative-germination rate and potential; the germinate rate was lower and potential was weaker at the concentration of 0.2% than at 0.1%. Under the same concentration, the relative- germination rate and potential reduced first then enhanced along with the increase of treating time. The treating time of 3 days had the lowest germinate rate and potential. Results of the second experiment showed that the tetraploid inducing rate was significantly different between the species and among the families within species. The average inducing rate was 3.76% for the four B. pendula families but was only 0.09% for the three hybrid families. The highest rate was 8.86% for YB3.