Diffusivities of Ti, Cu, Al and Ag in the interface of Al2O3-Al2O3 braze joints using Ag-Cu-Ti active filler alloy, have been calculated by Matano-Boltzman method. The Matano plane has been identified for each elemental diffusion at various brazing temperatures. The diffusivities of Ag, Cu and Al are almost insignificant on formation of interface during brazing, whereas the diffusivity of Ti changes significantly with the brazing temperature and controls the formation of different reaction product in the interface. Presence of TiO and Ti3Cu3O phases in the interface has been confirmed by transmission electron microscopy (TEM).