Amorphous structures of the as-cast bulk metallic glass samples (BMGs) of Cu 60 Zr 25 Ti 15 and (Cu 60 Zr 25 Ti 15 ) 95 Ni 5 alloys are confirmed by X-ray diffraction. Isothermal crystallization kinetics of these BMGs are investigated using differential scanning calorimetry. For both the alloys, the apparent activation energy ( E a ) shows a strong dependency on crystallization volume fraction ( x ). Isothermal crystallization kinetic parameters are calculated by Arrhenius and Johnson–Mehl–Avrami equations. Avrami exponential factor ( n ) is also found to show clear correlation with the crystallization volume fraction ( x ). It is found that the crystallization process is easier in Cu 60 Zr 25 Ti 15 BMG than in (Cu 60 Zr 25 Ti 15 ) 95 Ni 5 BMG as the E a decreases constantly for the former alloy though in the case of second alloy, the E a is almost unchanged up to x  = 60%. For both the alloys, nucleation activation energy ( E nucleation ) is found to be higher than that of growth activation energy ( E growth ). This indicates that the growth of crystals during isothermal crystallization in these glasses is easier than nucleation, and the minor addition of Ni causes the higher thermal stability against crystallization in isothermal condition.