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Furnace brazing of Ti-15Mo-5Zr-3Al (Ti-15-5-3, β-Ti) alloy using clad Ti-15Cu-15Ni foil as the filler in a high vacuum has been carried out. In the brazed joints, the chemical compositions of distinct phases were quantified by electron probe micro-analyzer (EPMA), and the phase structures were identified by electron backscatter diffraction (EBSD). The as-brazed joint composed of α-Ti, retained β-Ti, Ti₂Ni, and Ti₂Cu. The embrittlement of the brazed joint was correlated mainly with the formation of intermetallics, especially cellular Ti₂Ni dendrites in the brazed zone. It was noticed that the molten filler liquated the β-Ti grain boundaries and assisted the eutectic reaction therein, resulting in forming grain boundary Ti₂Ni surrounded by the retained β-Ti. The results indicated that proper brazing conditions were able to eliminate all the harmful phases effectively, and increased the shear strength of the Ti-15Mo-5Zr-3Al brazed joint.