Cu-Zr-Ti-Sn bulk metallic glasses were produced by copper mold casting. The effects of Sn addition on glass-forming ability (GFA), thermal stability of the Cu 6 0 Zr 3 0 Ti 1 0 bulk metallic glass were investigated. It was found that a bulk metallic glass of 5 mm in diameter was prepared in a (Cu 6 0 Zr 3 0 Ti 1 0 ) 9 9 Sn 1 alloy by copper mold casting. The addition of 1 at.% Sn is effective for an increase in GFA. The ΔT x and T g /T l are 46 K and 0.63, respectively, for (Cu 6 0 Zr 3 0 Ti 1 0 ) 9 9 Sn 1 alloy. With increasing the content of Sn, the value of T g /T l increases, but the alloys begin to lose bulk metallic GFA. The new parameter γ has a better correlation with the GFA of the Cu-based alloys.