Abstract: Analysis of genetic stability of transgenic lines is an important part of genetic engineering. In this study, we measured growth traits including thousand-seed weight, germination rate, germination potential and vigor index for offspring of transgenic birch . These offspring include families of control-pollination, reciprocal cross and half-sibling families of open pollination. The results showed that all these measured traits were significantly different among these families. Coefficients of variation of these growth traits varied from 41.09% to 73.16% and all the heritabilities were higher than 98.00%. Thousand-seed weight was significantly positively correlated with germination rate, germination potential and vigor index, and the corresponding coefficients of variation were 0.916, 0.803 and 0.896, respectively. Interestingly, we found that the foreign genes can be better inherited from female gamete than from androgamete. About 60.00% of offspring from female gamete harbored the foreign genes, while it was only 30.00% of offspring from androgamete. Investigation of the foreign genes of five offspring revealed that four of them had one insertion site, and one had two insertion sites. Chi-square testing of the offspring that had one insertion site indicated that the segregation ratio of gamete was 1∶1. For families which had two insertion sites, the ratio was 3∶1.