A new melting enthalpy ΔH m criterion for the prediction of glass forming ability (GFA) of alloys is proposed and five Zr–Al–Ni–Cu bulk metallic glasses (BMG) with critical dimension Z max up to ∅ 7.5mm are also developed by us in the light of the optimum ΔH m of Zr–Al–Ni–Cu alloy system. And then, we researched the relationships between ΔH m and two GFA parameters (critical cooling rate R c and Z max ) of five bulk metallic glass (BMG) systems, such as Mg–Ni–Nd, Pd–Cu–Si, La–Al–Ni–Cu, Zr–Al–Ni–Cu and Zr–Ti–Ni–Cu–Be, respectively. The results show that the relationships between ΔH m and R c are all concave upward parabolas, and the optimum ΔH m s for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.3960kJmol −1 , 21.2202kJmol −1 , 19.7146kJmol −1 , 18.1455kJmol −1 and 13.1558kJmol −1 , respectively. On the contrary, the relationships between ΔH m and Z max are all concave downward parabolas, and the optimum ΔH m s for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.5530kJmol −1 , 21.0830kJmol −1 , 19.6603kJmol −1 , 19.7231kJmol −1 and 13.1173kJmol −1 , respectively. Furthermore, other BMGs’ R c s or Z max s predicted by above-mentioned relationships satisfactorily agree with the tested results, which indicates that these relationships are reliable. However, the predicted results are reliable only if the main components are similar with the fitted BMGs or the additive is sparkle enough that the alloy’s character does not change. On the whole, the ΔH m can act as a criterion for quickly predicting the alloy’s GFA and be helpful for the development of new BMGs.