An efficient and repeatable approach in transforming the foxtail millet (Setaria italica ) using Agrobacterium LBA4404 horboring the plasmid pBI121 was established. Factors affecting transformation efficiency were investigated including the genotype, explants, the density of bacteria, the duration for inoculation and co-cultivation, and the concentration of acetosyringone in the medium. The maximum transformation conditions were: the callus induced from inflorescence was used as explant; the duration for inoculation with Agrobacterium at low cell density was 30-40 min; for the co-cultivation , the suitable concentration of acetosyringone in the medium was 0.1 mmol/L, and the duration was 2 days.