The quaternary Ti-Cu-Ni-Zr bulk metallic glasses are developed through proportionally mixing of the binary eutectic phases of Ti 27 Cu 73 , Ti 76 Ni 24 , Zr 38 Cu 62 and Zr 76 Ni 24 . The novel Ti-Cu-based bulk metallic glasses with the critical diameter of 4mm are successfully developed by the modification of the proportion of these eutectic units. The different glass forming ability (GFA) is discussed in a frame of thermodynamics. The GFA of these quaternary alloys correlate well with the reduced glass transition temperature (T rg ), the γ value, the reduced ideal glass transition temperature (T K /T m ) (where T K is the ideal glass transition temperature) as well as the ratio between specific heat and entropy differences ΔC p m /ΔS m at the melting temperature (T m ).