Single-phase (Zr/Ti)–Cu–Al–Ni metallic glasses were synthesized by copper mold casting and mechanical alloying of elemental powder mixtures. In addition, nanostructured metallic glass composites were produced by annealing of as-cast specimens and by mechanical alloying of elemental powder mixtures blended with different volume fractions of ZrC particles. For cast specimens, the effect of composition on the thermal stability and the microstructure after partial crystallization was investigated by X-ray diffraction and differential scanning calorimetry. Ti additions lead to a lower overall thermal stability of the material and induce primary crystallization. The grain size of the precipitates after the first crystallization stage becomes progressively finer with increasing Ti content, yielding grain sizes as small as about 2 nm for Zr_54.5Ti_7.5Cu₂₀Al₁₀Ni₈. For mechanically alloyed Zr₅₅Cu₃₀Al₁₀Ni₅ powders containing up to 30 vol% nanoscale ZrC particles, stoichiometry variations of the glass due to particle dissolution in the glassy matrix during the mechanical alloying process were observed, which affect the thermal stability of the glassy matrix phase. Nevertheless, the composites maintain an extended supercooled liquid region before crystallization.