Based on Zr₄₈Cu₄₈Al₄, a typical TRIP (phase transformation-induced plasticity)-ductilized bulk metallic glass composite (BMGC)-forming alloy, the effect of microalloying of Ti or Nb on its solidification microstructure and properties has been investigated. It is found that compared with the base alloy, microalloying significantly changes the microstructure of the reinforcing B2 phase which is embedded in the glass matrix and leads to the TRIP effect upon loading. In particular, Ti microalloying reduces the driving force for B2-nucleation, and improves the alloy’s glass forming ability and BMGC-forming range. On the other hand, Nb microalloying stabilizes the B2 phase, and significantly increases the hardness of the glass and the B2 phase, as well as the strength and compressive plasticity of bulk metallic glass composite (up to 1470MPa and 21.5%, respectively). This study has implications for the development of high-performance TRIP-ductilized bulk metallic glass composites.