[en] The thermodynamics and kinetics of glass forming melts are essential parameters for understanding the glass forming ability of materials. The Gibbs free energy difference (ΔG) between undercooled liquid and corresponding equilibrium solid plays an important role in nucleation and growth processes. Due to high thermal stability of undercooled melts of BMG glass formers the experimental data of thermodynamical parameters of bulk metallic melts are available over a wide range of undercooling and it is very interesting to study the thermodynamics of undercooled melts of BMGs. The aim of present work is to study ΔG of zirconium based BMG using an expression based on Taylor's series expansion. The enthalpy difference (ΔH) and entropy difference (ΔS) between the undercooled liquid and corresponding equilibrium solid phases is also studied. The importance of the Kauzmann temperature has also been discussed. The study is made for Zr_58.5^- Cu_15.6Ni_12.8Al_10.3Nb_2.8 in the temperature range T_m to T_g, where T_m and T_g are the melting and glass transition temperatures respectively. An attempt is also made to study the glass forming ability of BMGs.