Ga-MFI was synthesized by a hydrothermal process at atmospheric pressure. The effect of mole ratios of reactants on crystallization was also investigated thoroughly. The characteristics of synthesized Ga-MFI was compared with ZSM-5. The synthesis of Ga-MFI was carried out with five different mole-compositions of _aSiO2-_bGa2O3-_cNa2O-_dTPA2o-_eH2O. The synthesized Ga-MFI and ZSM-5 were characterized by XRD and FT-IR. The inorganic cation (Na+) and water played an important role in crystallinity and the organic cation (TPA+) as a template played a great influence on yields. With the increase in the amount of Ga3+, crystallization time was increased. With a fixed SiO2/Ga2O3 ratio of 400, the optimum reaction condition was obtained at H2O/SiO2=30~35, Na2O/SiO2=0.5~0.6, and TPA2O/Na2O=1~1.25. In these cases, the crystallinity and yield were more than 95% and 90%, respectively. By comparing IR spectrum of Ga-MFI with those of ZSM-5 and silicalite, it was found that Ga-MFI showed a unique peak at 970 cm-1, which may be used to identify Ga-MFI from ZSM-5 and silicalite.