Crystallization kinetics of Cu47Zr47Al6 and (Cu47Zr47Al6)99Sn1 bulk metallic glasses in the non-isothermal and isothermal conditions were investigated by differential scanning calorimetry (DSC). In non-isothermal condition, the crystallization activation energy was determined by various methods, and the Sn-containing glassy alloy showed higher crystallization activation energy than that of the base alloy, that means the Sn addition delayed crystallization transformation. In the isothermal condition, the Sn-containing BMG shows longer incubation time and wider crystallization transformation peak than that of the Sn free sample alloy, at the same annealing temperature. The time-temperature-transformation (TTT) diagram signified that the Sn addition delayed the crystallization and consequently improved the GFA. In isothermal conditions, the Avrami exponents vary from 3.75 to 5.31 and 3.88 to 4.08 for Cu47Zr47Al6 and (Cu47Zr47Al6)99Sn1 BMGs, respectively. According to Avrami's model, these numbers indicate that the crystallization of both glassy alloys is governed by three-dimensional growth with an increasing nucleation rate, while Sn addition decreases the nucleation rate.