In this article, our current understanding on the effects of Zr additions on the properties of three-phase Mo-Si-B alloys is reported. This novel group of materials having high melting points around 2000 C have been identified as potential alloy systems for structural applications at temperatures beyond 1200 C, e.g., for substituting or supplementing state-of-the-art nickel-base superalloys in the power generation industry. In earlier work, we developed various Mo-Si-B materials with very good high-temperature deformation behavior and, in addition, that satisfy oxidation performance. Minimum brittle-to-ductile transition temperatures of around 950 C, however, do not meet the requirements for high-grade stressed structural materials. Therefore, in a second trial, we investigate the influence of the alloying element Zr (which was already proven to increase the strength as well as the ductility of a single-phase Mo-Si alloy) on three-phase Mo-Si-B alloys.