Abstract: PCR amp lification was app lied on selectable marker gene neom ycin phosphotransferase II (N PT II) in twotransgenic pop lar species, P. ×euram ericana‘Guariento’and Populus alba ×P. glandulosa which contain one tofive foreign genes. The results showed that this gene was stable integrated in the genome of pop lar trees analyzed.To quantify the exp ression of N PT II gene, enzyme linked immunosorbent assay was performed on both transgenicpop lar species. The results showed highly significant linear correlation between quantity ofNPTII p roteins and theirOD values, while the quantity of NPTII p roteins exp ressed in different transgenic lines did not increase with theincreased number of transgenes in both pop lar species. Our results indicated that the potential biosecurity riskcaused by multip legenes transgenic pop larwas notmore serious than that of single gene transgenic pop lar.