The effect of BaF_2 flux in Y_3Al_5O_12:Ce^(3+)(YAG:Ce) formation was investigated. Phase transformation of Y_3Al_5O_12(YAG) was characterized by using XRD, SEM, and TEM-EDS, and it was revealed that the sequential formation of the Y_4Al_2O_9(YAM), YAlO_3(YAP) and Y_3Al_5O_12(YAG) in the temperature range of 1000-1500oC. Single phase of YAG was revealed from 1300℃. In order to find out the effect of BaF_2 flux, three modeling experiments between starting materials (1.5Al_2O_3−2.5Y_2O_3, Y_2O_3−BaF_2, and Al_2O_3−BaF_2) were done. These modeling experiments showed that the nucleation process occurs via the dissolution-precipitation mechanism, whereas the grain growth process is controlled via the liquid-phase diffusion route. YAG:Ce phosphor particles prepared using a proposed technique exhibit a spherical shape, high crystallinity, and an emission intensity. According to the experimental results conducted in this investigation, 5% of BaF_2 was the best concentration for physical, chemical and optical properties of Y_3Al_5O_12:Ce^(3+)(YAG:Ce) that is approximately 10-15% greater than that of commercial phosphor powder.