Non-isothermal change in electrical resistance was used to investigate the crystallization process of GaSb-Sb2Te3 pseudobinary films prepared by co-sputtering using GaSb and Sb2Te3 targets. The crystallization parameters were determined directly by in-situ electrical resistance-temperature measurements. The activation energy of crystallization and rate factor were deduced from the Kissinger's plot. The kinetics exponent was calculated using the Ozawa's method. The crystallization temperature (185-228 degrees C) and activation energy (2.01-5.65 eV) increased monotonically with increasing Ga concentration from 5 to 34 mol%, while the average kinetics exponent decreased from 1.63 to 1.02. The crystallization mechanism of the compositions with Ga concentration more than 10 mol% was one-dimensional growth from the nuclei due to the average kinetics exponent smaller than 1.5. Crystallization time of the studied compositions was estimated theoretically by the Johnson-Mehl-Avrami equation and measured experimentally by the reflectivity change induced by the laser pulse. It is shown that Ga27Sb47Te26 film exhibited the shortest crystallization time, suggesting a potential candidate for phase-change random access memory application.