Microstructural and mechanical property characteristics were investigated for three boride-dispersed composites fabricated by hot-pressing amorphous Ni60Mo30B10 powder. The first composite was tested in the as-hot-pressed condition (HP) whilst the other specimens were subjected to a solution treatment (ST) and further ageing (STA). X-ray diffraction showed the HP and ST composites to consist of Mo2NiB2 particles in a Ni-rich matrix whilst the STA material contained Mo2NiB2 particles in a NiB3Mo matrix. The hardness and fracture toughness decreased and increased, respectively, for the ST material compared to the HP case whilst the STA case showed increased and decreased hardness and fracture toughness, respectively, compared to the ST composite. These results were explained in terms of the brittle–ductile–brittle fracture modes for the HP–ST–STA specimens. In addition, the HP specimen showed only a 15% decrease in compressive strength at 973 K compared to 303 K.