In order to improve the gene transformation system for a lily variety, this report presents some research results that affected to gene transformation of Belladonna lily bulb scales slides via Agrobacterium tumefaciens. There are some major factors influencing transformation efficiency have optimized such as appropriate concentration of cefotaxime could kill the bacteria and unaffected the regeneration of sample, the threshold of hygromycine that help to select of transgenic plantlets, suitable bacteria strain with proper bacterial concentration and the suitable time of co-culture. The results show that the lily bulb scales slides were immersed with the EHA 105 strain carrying binary pCAMBIA1301 vector that contains the Gus gene and hygromycine resistance gene at a concentration of bacterial suspension OD600 from 0.6 to 0.9, around 30 minutes, then co-cultured for 3 days are the best. Continuously, samples were washed by sterilized fluid MS supplement with 500 mg/l cefotaxime and cultured on regeneration environment supplement with 250 mg/l cefotaxime to regenerate new bulblets. Transgenic bulblets initially could be selected on selective antibiotics medium with 75 mg/I hygromycine. Under the above conditions, efficient of gene transformation to lily were obtained relatively high efficiency, which is 8,8 percent (0,088 line / bulb scales slide).