Ag8In14Sb55Te23 (AIST) films are deposited on K9 glass substrates by DC magnetron sputtering. A pump-probe system is employed to observe reflectivity change process in real time. The results show that phase transition driven by nanosecond laser pulses can be achieved in a proper fluence range on AIST thin films. The presence of liquid phase is identified by transient reflectivity level between those of the amorphous and crystalline phases. Crystallization time and reflectivity change are linearly proportional to the energy at lower pulse fluences.