This paper reports the investigation on the crystallization kinetics of Zr6 0 Al15Ni25 bulk glassy alloy under isothermal annealin g by differential scanning calorimetry. The results show that the incubation time is very smal l even at a low annealing temperature (743 K) and the exothermic peak width, ref lecting the time for the actual crystallization process, increases greatly when annealing temperature decreases. This suggests a growth-controlled crystallizati on process. The Avrami exponents indicate that the crystallization mechanism cha nges at different annealing temperatures. The change of the crystallization mech anism is attributed to the great change of the mobility of atoms at different te mperatures.