Ternary Sm-based Sm-Al-Co alloys at specific compositions designed using an e/a- and cluster-related criteria exhibit high glass forming abilities and form bulk glassy rods of 3 mm in diameter by a copper mold suction-casting method. Four compositions of bulk metallic glasses (BMGs) are Sm₅₀Al₂₅Co₂₅, Sm₅₂Al₂₄Co₂₄, Sm₅₄Al₂₃Co₂₃ and Sm₅₆Al₂₂Co₂₂, which all satisfy a constant conduction electron concentration of 1.5. Among them, the BMG exhibiting the largest reduced glass transition temperature (T_rg) is Sm₅₀Al₂₅Co₂₅, which reaches 0.648. The glass transition temperature T_g and the onset crystallization temperature T_x of this alloy are respectively 579 and 640 K at a heating rate of 20 K/min.