Abstract: The bulk metallic glass formation in the Cu-Zr-M ternary systems by alloying of a binary basic Cu₆Zr₅ cluster was investigated, where M stands for Sn, Mo, Ta, Nb, Ag, Al and Ti. The Cu₆Zr₅ cluster is a capped Archimedean antiprism that characterizes the local structure of the Cu₁₀Zr₇ crystalline phase. This cluster composition almost superposes with Cu-Zr eutectic Cu_0.56Zr_0.44. A series of alloys along the cluster line (Cu₆Zr₅)_1-xM_x were examined for their glass forming abilities. Alloy rods with a diameter of 3 mm were prepared by copper mould suction casting method and analyzed by XRD and thermal analysis. The Cu-Zr based bulk metallic glasses were discovered with minor Nb, Sn, Mo, Ta additions (≤2at%) and Al, Ti, Ag (8at%≤concentration≤9at%). The alloying mechanism was discussed in the light of atomic size, cluster-linking structure and electron concentration factors.